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Why Does My Energy Fluctuate So Much? A Sleep MD Explains

Your energy fluctuates throughout the day because of your body clock. Sleep debt, food, and activity make it fluctuate more, and sleep timing and light affect the timing.
Published
2021-11-23
Updated
2023-10-20
18 MINS
Written by
Jeff Kahn, M.S., Rise Science Co-Founder
Reviewed by
Chester Wu, MD, Rise Science Medical Reviewer
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We bring sleep research out of the lab and into your life. Every post begins with peer-reviewed studies — not third-party sources — to make sure we only share advice that can be defended to a room full of sleep scientists.
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Updated Regularly
We regularly update our articles to explain the latest research and shifts in scientific consensus in a simple and actionable way.
Woman wondering why her energy fluctuates so much

Why Does My Energy Fluctuate So Much Throughout the Day?

  • Your energy levels fluctuate throughout the day due to your circadian rhythm, or body clock. 
  • Sleep debt, diet, exercise, your sleep schedule, and light exposure can affect when and by how much your energy fluctuates. 
  • The RISE app can predict when you’ll feel peaks and dips in energy each day and help you get more energy overall.

In the morning, you’re alert and smashing through your to-do list, but come the afternoon you can’t keep your eyes open. Then by 6 p.m., you’re buzzing again. Even more confusing? When these peaks and dips in energy happen at different times the next day and are unpredictable throughout the week. What gives? 

The main reason your energy levels fluctuate so much is due to your circadian rhythm, or body clock. Other factors — like sleep deprivation, sleep timing, light exposure, exercise, and food — can add to these ups and downs in your energy and change when they happen. 

Read on to find out what makes your energy fluctuate so much, how to make your energy more predictable, and how you can use the RISE app to plan for these changes and get more energy overall.

A Sleep Doctor Explains

“Your energy levels rise and fall across the day as part of your circadian rhythm, or body clock. You’ll naturally feel groggy when you first wake up, feel more energetic in the morning, have an afternoon slump, and then a second wind in the early evening. Getting enough sleep can make these fluctuations in energy feel better and higher and a consistent sleep schedule can make the timing of your energy fluctuations more predictable.”

Rise Science sleep advisor and medical reviewer Dr. Chester Wu

Why Does My Energy Fluctuate So Much? 

Your energy levels fluctuate across the day and these peaks and dips in energy can happen at different times and by different amounts. Here’s why:

  • Your energy fluctuates in a predictable pattern throughout the day because of your circadian rhythm, or body clock. You’ll feel groggy when you first wake up (known as sleep inertia), feel more energetic in the morning, have an afternoon slump, and a second wind in the early evening, before winding down for sleep.
  • Sleep debt, ultradian rhythms, exercise, and what and when you eat and drink can make your energy fluctuate even more, affecting both the amount of energy you feel and when it rises and falls. 
  • Your sleep schedule and when you get light exposure can shift the timing of your circadian rhythm, therefore shifting the timing of when your energy rises and falls. But your energy will still follow a predictable pattern. 

Let’s dive into all of those factors in more detail. 

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Your Circadian Rhythm 

Your circadian rhythm, more commonly known as your internal body clock, dictates when every cell in your body is at work and at rest over the rough span of 24 hours. 

Your circadian rhythm is the main reason why your energy fluctuates throughout the day.

It dictates your sleep-wake cycle, when your body makes certain hormones like cortisol to make you feel alert and melatonin to make you feel sleepy, when your body temperature fluctuates, and, as a result, when your alertness, performance, and energy levels are at their highest — and lowest — throughout the day.

RISE app can determine your circadian rhythm
Caption: Your circadian rhythm follows a predictable roughly 24-hour cycle. Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6123576/

It’s normal for your energy levels to fluctuate. In fact, they follow a predictable pattern each day.

Here’s what energy levels normally look like: 

  • You wake up and feel sleep inertia, or grogginess 
  • You have a peak in energy around mid-morning
  • You have a dip in energy, known as the afternoon slump
  • You have another peak in energy around the early evening
  • Your energy winds down until bedtime 

It’s not just your energy levels that go up during your peaks. Research shows your attention, emotional regulation, mood, accuracy, reaction time, and learning ability can be higher, too. 

And during your dips, you’ll feel lower on energy and may find your mood, motivation, and even your ethics take a hit. It might also feel like you’ve got brain fog during these times. An interesting exception? Research suggests you may be better at solving problems that need insight or creativity during your dips in energy.

The timing of your circadian rhythm — and therefore when your energy levels rise and fall — is dictated in part by your chronotype. This is whether you’re an early bird, night owl, or something in between. An early bird will have their energy peaks and dips earlier in the 24-hour cycle than a night owl. 

All this may sound complicated, but RISE can predict the timing of your circadian rhythm each day and show you when your energy levels are expected to rise and fall. 

RISE app screenshot showing your energy  peak and dip times
The RISE app can predict when your energy levels will fluctuate.

Getting Out of Sync With Your Circadian Rhythm 

When you’re out of sync with your circadian rhythm, your energy levels will still fluctuate, but they can be lower overall and your peaks and dips can happen at inconsistent times. 

You can get out of sync with your circadian rhythm by: 

Your body might be producing cortisol (which makes you feel alert), dopamine (which is linked to pleasure and motivation), and melatonin (which primes you for sleep) at the wrong times. This can mean you wake up tired or feel wired at bedtime. You may find yourself falling asleep randomly during the day and missing out on sleep at night — leading to lower energy. 

To make things more complicated, there’s more than one clock that can get out of sync. You have your central clock, which controls your sleep-wake cycle, and you have clocks in almost every tissue and organ in your body, including your liver, digestive system, and immune system. These are known as peripheral clocks

These clocks can get out of sync with your central clock. If you eat at irregular times, for example, your digestive clock can get thrown off course (which is why we often have digestive issues when traveling across time zones). 

Circadian misalignment (when you’re out of sync) can lead to low energy, impaired mental performance, more procrastination, weight gain, and physical and mental health problems. 

It can increase your risk of heart disease, type 2 diabetes, obesity, depression, and attention deficit disorders — all of which can affect your energy levels.  

Heads-up: The timing of your circadian rhythm can change from day to day (more on that soon), but it also shifts across your lifetime. Teenagers are usually more night owls, so the timing of their energy fluctuations will skew later in the day. As we age, our circadian rhythms tend to shift earlier, so we become more natural early birds with energy peaks and dips earlier in the 24-hour cycle. Our circadian rhythms also flatten as we age, so the cues for when to go to sleep and wake up aren’t as strong and energy peaks and dips are naturally more muted. 

RISE users on iOS 1.202 and above can see their upcoming energy peaks and dips on the Energy screen here.  

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Sleep Debt 

Sleep debt is the amount of sleep you owe your body. It’s measured against your sleep need, which is the unique amount of sleep you need a night. 

If you haven’t been getting enough sleep recently, you’ll have sleep debt and will feel low on energy throughout the day. 

Together, sleep debt and circadian rhythm are the two biggest factors influencing your energy levels each day. They independently impact your energy levels and affect each other.

Your circadian rhythm keeps ticking away even when you’ve got sleep debt. But those dips in energy will feel worse when you’re sleep deprived, meaning you might find it much harder to get out of bed, make it through the afternoon without a caffeine hit, or simply want to sleep all the time. And your peaks in energy won’t be as high as they could be.

When you get more sleep, you’ll probably find your energy levels pick up again. 

It’s not all about how much sleep you get, though. Unbroken sleep is more restorative than restless sleep. And how you feel about your sleep matters, too. A 2022 study found more light sleep and less time awake at night is linked to being more satisfied with your sleep. And research from 2021 found how people feel about their sleep has a bigger impact on fatigue than sleep duration.

Heads-up: Everyone needs a different amount of sleep, and the range might surprise you. When we looked at how much sleep 1.95 million RISE users need, sleep needs ranged from five hours of sleep to 11 hours 30 minutes.

The RISE app can tell you how much sleep you need.
The RISE app can tell you how much sleep you need.

RISE can work out how much sleep you need and whether you’re carrying any sleep debt. 

RISE users on iOS 1.202 and above can click view their sleep need here and view their sleep debt here.

Ultradian Rhythms 

Ultradian rhythms are shorter rhythms than your full 24-hour circadian rhythm. When it comes to your energy, ultradian rhythms usually last about 90 minutes. 

You may notice you can speed through your to-do list in high-energy mode for an hour or so before needing a break before the next 90-minute burst of energy. 

You can learn more about ultradian rhythms and how to focus here.

Diet 

What you eat can influence how much your energy levels fluctuate throughout the day. 

Sugary snacks and simple carbs like white bread can spike your blood sugar levels, giving you a sugar rush. But you’ll soon get hit with the sugar crash and a rapid drop in your energy levels. 

Nutritional deficiencies such as a vitamin D, vitamin B12, or iron deficiency can cause tiredness. 

On the other hand, a balanced diet of fruits, veggies, and complex carbohydrates (like oatmeal and brown rice) can give you a steady release of energy over the course of the day. 

We’ve covered more foods that give you energy here.

Your diet can also make the peaks and dips in your circadian rhythm feel better or worse.

Research shows a heavy lunch can make you feel sleepier and perform worse during your afternoon dip in energy.

A 2022 study found a breakfast rich in complex carbs was linked to higher levels of alertness in the morning compared to a breakfast with moderate carbs, proteins, and fats. A high-protein breakfast was linked to lower alertness compared to the moderate breakfast. 

And another study found school kids who ate breakfast performed better than those who skipped breakfast. Kids who ate more whole grains in the morning performed much better in reading, fluency, and math tests, whereas those who had fruit juice performed worse.  

When it comes to drinks, caffeine can give you an energy boost whereas alcohol can first act as a stimulant and then make you feel drowsy. And both of these drinks can disrupt your sleep if you consume them too close to bedtime. Dehydration can cause fatigue and drinking water too close to bedtime can lead to middle-of-the-night bathroom trips. 

If you eat dinner close to bedtime, you can also have trouble falling and staying asleep. This can cause sleep debt to build up, lowering your next-day energy levels. 

In general, avoid eating two to three hours before bed

You may even want to finish eating earlier than this. A 2023 study found time-restricted eating (when you eat within a certain window of time, such as between 8 a.m. and 8 p.m.) was linked to getting more sleep and sleeping earlier.

RISE can tell you when to have your final meal, cup of coffee, and alcoholic drink each day to stop them from messing with your sleep and energy levels. 

RISE app screenshot showing when to have your last big meal
The RISE app can tell you when to stop eating before bed.

RISE users on iOS 1.202 and above can set up their avoid late meals reminder here.

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Exercise 

Exercise is almost always good for your energy levels and your sleep. 

In the short term, it can increase your heart rate, blood flow, and endorphins for an energy boost. And in the long run, it can help to increase your energy levels. Exercise can lower your stress levels and help with weight loss, which can help you get a good night’s sleep, too. 

A 2022 study found more physical activity during the day leads to more energy the next morning. And a 2023 systematic review found regular exercise can help you fall asleep faster and improve your sleep quality.

Working out on no sleep may even mitigate some of the short-term negative impacts of sleep loss (although more research is needed).  

If you don’t exercise, or have recently stopped because of an injury or a busy work schedule, your energy levels may be lower. Or you might notice on the days you work out, your energy levels are higher. 

Exercise can also make those dips in energy first thing and during the afternoon feel more manageable to help stabilize your energy across the day. 

One study found just 30 seconds of exercise can help you shake off sleep inertia in the morning. And another study found a 10-minute walk can boost your energy more than eating a candy bar. 

On the other hand, exercising too much can tank your energy levels, so make sure you’re taking those rest days. 

Exercising during the day is best. Intense exercise within an hour of bedtime can keep you up. RISE can tell you when it’s best to skip a workout or opt for something gentle like yoga before bed. 

Your Sleep Schedule 

How much we sleep affects our energy levels, but when we sleep also makes a difference. 

If you have an inconsistent sleep schedule, you’ll throw your circadian rhythm and the predictability of your energy levels off track. This can happen if you’re working night shifts or rotating shifts, or if you simply stay up and sleep in later on weekends compared to during the week.

This is known as social jetlag and it’s common. About 87% of us have it and go to bed at least two hours later on the weekend. 

When you’ve got an inconsistent sleep schedule, you’ll still experience those peaks and dips in energy as part of your circadian rhythm, but they’ll happen at different times each day, depending on when you went to sleep and woke up. 

So your energy can be lower overall and it’ll fluctuate unpredictably across the week.

Having a consistent sleep schedule, on the other hand, can help to keep the timing of your energy fluctuations more consistent and predictable day to day.

Light Exposure 

The timing of your circadian rhythm isn’t set in stone. It can be changed by something called a zeitgeber. Zeitgebers, German for time-givers, are external cues that time your circadian rhythm with the outside world. 

Zeitgebers include: 

  • Light exposure (the most powerful one)
  • Temperature 
  • Meals
  • Exercise
  • Social interactions 

A zeitgeber can either bring the timing of your circadian rhythm forward or push it back, depending on when in the 24-hour cycle you’re exposed to it.

For example, if you get light exposure late at night, you can push back your circadian rhythm, pushing back when you’ll feel sleepy and alert. If you get it early in the morning, you can bring forward the timing of your circadian rhythm, meaning those peaks and dips will happen earlier than usual. 

Getting light exposure, eating, and exercising at roughly the same times each day can keep your circadian rhythm running smoothly, meaning your energy fluctuations will happen at roughly the same times across the week

You should get out in light as soon as possible after waking up and at a consistent time each day to reset your circadian rhythm, and avoid light in the run up to bedtime to make sure you don’t push back your circadian rhythm. 

You can learn more about when to get light exposure here for the best sleep, energy, and health. 

Heads-up: If you find you’re always tired, a sleep disorder or medical condition may be to blame. Insomnia, sleep apnea, chronic fatigue syndrome, depression, anemia, high blood pressure, and thyroid problems like hypothyroidism can leave you with a lack of energy. Medications can also cause sleepiness as a side effect. Talk to your healthcare provider to rule out any underlying causes. 

Beyond health conditions, allergies, air quality, wildfire smoke, stress levels, and hormones can all fluctuate from day to day, causing your energy levels to fluctuate too.  

How to Manage Your Energy Levels? 

It can be hard to know when a peak in energy is coming up and when a dip is about to hit, especially if your sleep schedule is all over the place.

RISE works as a personal energy tracker and can predict the timing of your energy peaks and dips each day. This way, you’ll never miss a productivity peak and won’t be caught out when your energy drops. 

You can integrate RISE into your Apple or Google calendar to align your daily energy fluctuations with your tasks and meetings.

For example, you can schedule your most demanding tasks — like coding, giving a sales presentation, or doing a demanding HIIT workout — for your peaks in energy. 

Easier tasks — like errands, emails, taking a nap, or going for a walk — can be scheduled for your dips in energy. 

RISE can also find the best time in your calendar to do energy-boosting activities like going for a walk or getting out in natural light. 

You can also check your sleep debt each morning to know whether you can expect your energy levels to be higher or lower, and make some healthy lifestyle changes to your diet and exercise routine to boost your overall energy. 

Plus, remember to keep your sleep schedule as consistent as possible and get light in the morning and avoid it before bed to make your energy fluctuations more predictable from day to day.

You can learn how to be more productive here and when you’re most productive here.

RISE app screenshot showing different ways to get an energy boost
The RISE app can help you schedule energy-boosting activities into your day.

 

How to Stop Energy Levels Fluctuating? 

You can’t stop your energy levels from fluctuating exactly, but you can make the dips feel more manageable, the peaks feel more powerful, and the timings of both more consistent. 

Here’s how to get more energy

  • Pay down your sleep debt: We recommend keeping your sleep debt below five hours for maximum energy. This is one of the best things you can do to boost energy. You can pay back sleep debt by taking short afternoon naps, going to sleep a little earlier than usual, and sleeping in a little later.
  • Get in sync with your circadian rhythm: Keep a regular sleep schedule (even on weekends), try to eat your meals at roughly the same times, and get out in sunlight as soon as you can each morning and avoid light before bed. If your circadian rhythm doesn’t match your daily life (perhaps you need to be up earlier for work), you can learn how to reset your circadian rhythm here to shift it earlier or later. Research shows a consistent sleep schedule can help you feel more energy overall, even if you get the same amount of sleep on an inconsistent schedule — and your energy will rise and fall more predictably. Plus, RISE users with consistent sleep patterns have lower sleep debt than those with inconsistent patterns — and lower sleep debt equals more energy.
  • Eat a healthy diet: Swap processed foods and sugary snacks for fruits, veggies, whole grains, proteins, and healthy fats, and make sure you’re drinking enough water. You can enjoy caffeine, but check RISE to see when you should stop drinking it each day. Research from 2022 says diets rich in fiber, fruits, vegetables, and anti-inflammatory nutrients and low in saturated fats are linked to better sleep quality. Talk to a healthcare professional or a nutritionist about supplements if needed. 
  • Do energy boosters during your dips in energy: Reduce feelings of fatigue by going for a brisk walk or a full workout, taking a cold shower, playing your favorite music, or taking a nap. We’ve covered more ways to feel more awake here. 
  • Improve your sleep hygiene: Sleep hygiene is the name for the daily behaviors that influence your sleep. With better sleep hygiene, you’ll have an easier time falling asleep, getting unbroken sleep, keeping your sleep debt low, and staying in sync with your circadian rhythm. Good sleep hygiene includes keeping your bedroom cool, dark, and quiet, getting out in sunlight in the morning, and dimming the lights about 90 minutes before bed.

RISE can guide you through 20+ sleep hygiene habits and tell you the best time to do each one based on your circadian rhythm that day. 

RISE app screenshot showing sleep hygiene habit reminders
The RISE app can guide you through 20+ sleep hygiene habits.

RISE users on iOS 1.202 and above can set up their 20+ in-app habit notifications here

Get More Consistent Energy Throughout the Day 

It’s natural for your energy levels to wax and wane as the day goes on. This is due to your circadian rhythm. Sleep debt, diet, and exercise can influence how high your energy is overall and when it rises and falls. And the timing of your sleep and light exposure can shift when these peaks and dips happen.  

RISE can help you get higher and more stable energy levels. The app can predict your circadian rhythm each day, so you know when your energy peaks and dips will be. And it’ll help you get in sync to give your energy levels a boost and make them more consistent day to day.

RISE also works out how much sleep debt you have and keeps track of it as you pay it back. This will make your energy peaks more potent and dips more manageable. 

Finally, RISE can guide you through 20+ good sleep habits to help you get a better night’s sleep for more energy.

It can happen fast — 80% of RISE users report more energy within five days of using the app. 

FAQs

Why does my energy fluctuate so much?

Your circadian rhythm, more commonly known as your internal body clock, dictates when every cell in your body is at work and at rest over the rough span of 24 hours. Your circadian rhythm is the main reason why your energy fluctuates throughout the day. Across the week, an irregular sleep schedule and being exposed to light at different times can change when your energy levels fluctuate.

Why do my energy levels fluctuate throughout the day?

Your circadian rhythm, more commonly known as your internal body clock, dictates when every cell in your body is at work and at rest over the rough span of 24 hours. Your circadian rhythm is the main reason why your energy fluctuates throughout the day. Sleep debt, sleep timing, light exposure, diet, and exercise can also influence when and how your energy levels fluctuate.

Why do my energy levels just drop?

Your energy levels can drop because of your circadian rhythm, or body clock. This causes your energy to fluctuate, being higher in the morning and early evening and lower in the afternoon. Your energy may also drop because of a sugar crash, dehydration, or lack of sleep. Inconsistent sleep times and badly timed light exposure can make your energy drop at different times day to day.

What affects energy levels?

Energy levels are affected by how much sleep you get, how in sync you are with your circadian rhythm, sleep timing, light exposure, diet, exercise, medical conditions, medications, and hormones. Your energy levels will naturally fluctuate across the day as part of your circadian rhythm and they’ll be lower if you don’t get enough sleep.

How do you track your body's energy level?

You can track your body’s energy level by noting down the time and how much energy you feel for several days. The RISE app can help you stay ahead of your energy levels by predicting when your energy will rise and fall each day and guiding you through steps to get more energy and make it more consistent.

Inconsistent energy levels ADHD

ADHD can cause restlessness, trouble concentrating, and sleep problems, which can cause inconsistent energy levels. Get more consistent energy with ADHD by making sure you’re getting enough sleep and syncing up with your circadian rhythm.

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