Sometimes it feels like a drug. It washes over you like a wave, and you feel your eyelids getting heavier and heavier as the urge to sleep grows stronger.
Whether you interpret drowsiness as a good feeling or a bad feeling probably depends on when and where it begins to take effect.
But as much as we might prefer to have non-stop energy all day until we’re ready for sleep at the end of the night, that’s not actually how our bodies work. Having peaks and dips in energy is a normal part of your circadian rhythm or internal clock.
Using a tool like the RISE app can help you get to know your unique circadian rhythm and figure out if your energy lulls are part of your predictable pattern or if your drowsiness is excessive and potentially problematic.
In this article, we’ll explore drowsiness as a biological process and explain the potential causes of excessive daytime sleepiness. We’ll also share some sleep hygiene tips that will help you get the sleep you need so you can have energy when you need it most.
Note: This article is for informational purposes only. See a doctor or healthcare professional for medical advice about suspected sleep disorders or other medical problems.
When you feel sleepy or drowsy, melatonin and adenosine are probably at play. Adenosine is a naturally occurring compound that builds up in the brain and causes sleepiness. Melatonin is a sleep-inducing hormone produced by the brain’s pineal gland. Each of these substances plays an important part in the two-process model of sleep regulation that we call The Two Laws of Sleep.
The Two Laws of Sleep are sleep homeostasis and circadian rhythm. These two processes work synergistically to govern your sleep-wake cycle.
Sleep pressure is the gradual buildup of adenosine in the brain. The more adenosine accumulates, the sleepier you feel — until the drive to sleep gets so strong (ideally, at the end of the evening) that you can barely keep your eyes open.
Sleep homeostasis is like a seesaw that wants to be level. As sleep pressure builds during the day, the seesaw gets more and more unbalanced. Going to sleep at night helps purge the brain of adenosine so that when you wake up in the morning, the seesaw is balanced. And the process repeats. But when you don’t get the hours of sleep your body needs, the seesaw doesn’t get completely balanced, and you accumulate sleep debt.
Sleep debt is the amount of sleep you’ve missed during the past 14 days, as compared to the sleep your body needed. Daytime sleepiness is one of the most common effects of high sleep debt.
The other process that plays a part in your sleep-wake cycle is your circadian rhythm. This internal clock dictates the peaks and dips in your energy levels — including your ideal wake time and bedtime — in roughly 24-hour cycles. And the timing of your light exposure is key to circadian alignment.
Inside the brain’s hypothalamus, there’s a special group of neurons called the suprachiasmatic nucleus (SCN) that’s attuned to the roughly 24-hour cycle of changing light caused by the Earth’s orbit around the sun.
When you wake up and the SCN senses daylight, it releases cortisol, norepinephrine, and serotonin — hormones that increase feelings of wakefulness and alertness. In the evening, the SCN responds to darkness by prompting the pineal gland to secrete melatonin, which causes drowsiness, or somnolence, and helps prep the body for sleep.
Your circadian rhythm also dictates the rest-activity cycle, which is a series of energy peaks and dips throughout the day. So it’s natural to feel somewhat sleepy at other times of the day — during your mid-day energy dip, for example.
And in the morning as you transition out of sleep, the grogginess you feel is called sleep inertia. That lingering sleepiness is caused by adenosine that wasn’t completely flushed out during the night. (Caffeine helps you feel more alert because it temporarily blocks adenosine receptors in the brain.)
When you consistently meet your sleep need, it usually takes 60 to 90 minutes for the effects of the adenosine residue to dissipate. But if you’re regularly sleep deprived and carry high sleep debt, this period of morning sleep inertia will be longer and feel more intense. And you’re more likely to feel drowsy throughout the day because you didn’t sleep long enough for all of the accumulated adenosine to burn off.
Even though there are these predictable dips in energy, circadian misalignment can also cause drowsiness. So it’s important to work with your body’s circadian rhythm and maintain circadian alignment (more on this later).
Getting to know your body’s circadian rhythm will help you figure out if your daytime drowsiness can be attributed to predictable dips in energy — the morning grogginess zone, the afternoon dip, and the evening wind-down — or if it’s being caused by something else that might need investigating.
Most drowsiness can be attributed to your predictable circadian energy dips at certain times of day, which is natural, or to high sleep debt or circadian misalignment, which is the result of poor sleep hygiene. But feeling drowsy all day is not normal. If you’re dealing with an ongoing struggle to keep your eyes open, a sleep disorder or other medical condition might be to blame.
Excessive daytime sleepiness (hypersomnia) is a primary symptom of many sleep disorders since the disrupted sleep and nighttime wakefulness often associated with these disorders usually results in high sleep debt.
Left untreated, sleep disorders like narcolepsy, sleep apnea, obstructive sleep apnea, and restless leg syndrome can negatively impact sleep and next-day energy levels, which can lead to other health problems. (A sleep medicine specialist can help properly diagnose and treat a sleep disorder.)
Likewise, circadian rhythm sleep disorders — the result of severe circadian misalignment — can cause drowsiness at inappropriate times.
Shift workers sometimes suffer from shift work disorder because their sleep schedules are often in conflict with their bodies’ natural circadian tendencies. And anyone traveling across multiple time zones can experience jet lag disorder because the body has a hard time adjusting to a new time zone as quickly as the flight can land you there.
Taking sleeping pills or tranquilizers as sleep aids can backfire, as their sedative effects can linger into the next day. Drowsiness is a common side effect of other medications, including certain types of antihistamines, antidepressants, and pain medications. Medical conditions like hypertension (high blood pressure), hypothyroidism, and hyponatremia (low sodium levels) can also cause excessive drowsiness.
Getting proper treatment for a sleep disorder or other underlying medical problems may help alleviate excessive drowsiness, but even mild daytime sleepiness can be cause for concern.
Experiencing any level of sleepiness during the day — at a time other than your afternoon dip — is something you should address. As professor and sleep medicine pioneer Dr. William Dement put it, “Drowsiness is red alert.”
That’s because what may feel like a little bit of drowsiness to you is likely already having a negative impact on your cognitive function, emotional health, and physical performance. When you accumulate high sleep debt, the brain adapts to functioning at a reduced capacity. After a while, your downgraded performance will start to feel normal even though, objectively, things are in decline.
At the societal level, drowsy people are dangerous people. If you’re driving or performing other functions that could endanger your life and the lives of others, being sleepy becomes literally life or death. Drowsy drivers are 10 times more likely to be involved in a car accident than reasonably alert motorists, and physicians are much more likely to make medical errors when they’re sleep deprived.
Sleep insufficiency is a problem that has become so widespread over the last few decades that it was recently declared a “public health epidemic” by the Centers for Disease Control (CDC). Even carrying moderate to high sleep debt (five hours or more) can have serious consequences. Short term, or acute, sleep debt — the 14-day version you can track with the RISE app — negatively impacts your cognition, emotions, attention span, reflexes, metabolism, immune system, and more.
And people who struggle with more chronic sleep deprivation have an increased risk for obesity, Type 2 diabetes, high blood pressure, heart disease, dementia, psychiatric disorders, cancer, and other chronic diseases.
The good news? For the most part, we can thwart the scourge of drowsiness in our lives by prioritizing sleep and improving sleep hygiene to lower sleep debt.
Because the most common cause of daytime drowsiness is not getting enough sleep at night, the best way to avoid sleepy days is to lower your sleep debt. That starts with improving your sleep hygiene with your circadian rhythm in mind.
Follow these guidelines for better sleep and better days.
To maintain circadian alignment and proper melatonin production, be strategic about the timing of your light exposure. Expose yourself to sunlight soon after waking, and eliminate or limit light exposure, especially bright light and blue light, in the 90 minutes before bedtime. (Blue-light blocking glasses are a good workaround solution when you can’t cloister yourself in the dark.)
Finally, make sure no light seeps into your sleeping environment. Use blackout curtains and an eye mask so you can sleep in complete darkness.
Exercise daily — it can help you get the sleep you need at night. And avoid consuming alcohol and caffeine, both known sleep disruptors, in the later afternoon or evening. (The RISE app can remind you of these cutoff times.)
Make Sleep a Matter of Routine.
Stick to a consistent bedtime and wake time for better circadian alignment, and institute a nightly wind-down period to disconnect from the stress of your day.
Listen to calming music, read a chapter of a novel, or take a warm bath or shower. Since your core temperature needs to drop in preparation for sleep, the way the body releases heat when you get out of the warm water helps accelerate this process and smooths your transition into sleep.
And to decrease nighttime awakenings, keep your bedroom at 65-68 degrees, the ideal temperature for sleep.
Who doesn’t love getting that fuzzy, drowsy feeling right as you slip into your PJs for the night? It tends to imbue a quiet confidence and hopefulness that you’ll be able to easily sleep through the night and wake up with ample energy to tackle your day.
But persistent daytime drowsiness is another story. This story is full of lost productivity, lackluster work performance, and miserable brain fog.
The best way to have more of the former and less of the latter is to maintain circadian-friendly sleep hygiene habits that will help you keep your sleep debt low and your daytime energy high. If that sounds like a tall order, fear not. RISE can help!
Our app will give you a clear picture of your circadian rhythm, keep track of your sleep debt, and send timely reminders to help you stick with your sleep hygiene habits. Because sleeping better means feeling better.
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