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Sleep Deprivation Stages and Why Sleep Debt Matters More

There are five stages of sleep deprivation, but acute and chronic sleep debt are more helpful when looking at everyday sleep loss. Here’s how to avoid them.
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Jeff Kahn, M.S., Rise Science Co-Founder
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Coping, struggling, suffering, losing it. Though hardly a scientific classification of sleep deprivation stages, those words in that order paint a picture of what it can feel like as hours of sleep loss begin to add up over days or weeks. 

In medical studies, sleep deprivation is often measured in 12- to 24-hour windows: 24 hours of sleep deprivation, followed by 36, 48, 72, and eventually, 96 hours without sleep. However, most of us will never experience the later stages of sleep deprivation. Acute and chronic sleep debt, on the other hand, are all too common.

Taking into account the low energy, decline in cognitive function, and medical problems associated with even low-level sleep deprivation — the effects of mounting sleep loss are alarming. The good news? It is possible to catch up on sleep. 

In this article, we’ll explain the different stages of sleep deprivation and explore the differences between acute sleep debt and chronic sleep debt . Plus, we’ll cover how the RISE app can help you adopt better sleep hygiene habits to reduce your sleep debt and increase your daytime energy levels.

What is Sleep Deprivation?

Sleep deprivation happens when you don’t get enough sleep. This could be caused by things like stimulants, shift work, or sleep problems keeping you up, or it could be a choice as you socialize or engage in sleep procrastination late into the night. Either way, if you don’t meet your sleep need, you’ll be sleep deprived. 

Your sleep need is the amount of sleep your body needs each night. It’s determined by genetics — just like your height and eye color — and it’s not simply eight hours for everyone. In fact, the average sleep need is 8 hours 10 minutes, plus or minus 44 minutes or so, but 13.5% may need 9 hours or more sleep a night.

And while a little bit of sleep deprivation isn’t serious, getting too much can make you feel awful and take a toll on your physical health and mental health. In fact, sleep deprivation was used as a form of torture as far back as 17th century England and it  was one of the "enhanced interrogation techniques" used at Guantanamo Bay starting in 2003. Detainees would commonly experience cognitive impairment followed by slurred speech and sometimes hallucinations and paranoia.

But why does lack of sleep wreak such havoc and misery? It seems to be something akin to inadequate waste removal.  In 2013, Dr. Maiken Nedergaard and her team at the University of Rochester Medical Center discovered a system that drains waste products from the brain.They named it the glymphatic system. It’s a cleanup system that’s most active during sleep and uses cerebrospinal fluid to flush away toxic byproducts that accumulate between cells. 

The longer you go without sleep, the more these waste products pile up, and the lousier you feel. Perhaps that’s why sleep loss is sometimes considered to be a kind of low-level brain damage. A recent study from Ohio State found that sleep loss resembles symptoms of a concussion

What Are the Sleep Deprivation Stages?

Have you ever wondered how long you can go without sleep? The longer you’re awake, the more intense and serious the negative impacts of sleep deprivation get, so you may not make it far. Here is a breakdown of the symptoms of sleep deprivation by the hour. (It’s worth noting that you don’t have to go long periods without sleep to feel these effects. Gradual sleep deprivation over multiple nights can cause similar impairment and damage. More on this later.)

The Starting Stage: After 16 Hours Without Sleep

Any amount of sleep that’s shorter than your sleep need will leave you sleep deprived, and the side effects will soon start to appear. The same goes for staying awake just slightly longer than usual. 

In his book, Why We Sleep, Matthew Walker explains, ”the recycle rate" of the human brain is around 16 hours. Stay up past that, and your brain is no longer working optimally. It’s becoming an overflowing trash can. And after 18 hours without sleep, you’ll suffer the same level of cognitive impairment as a person with a blood alcohol level (BAC) of 0.05%. 

Stage 1: After 24 Hours Without Sleep

It’s almost impossible to feel and perform at your best the day after pulling an all-nighter. In fact, going 24 hours without sleep results in cognitive impairment equivalent to having a BAC of 0.10%, higher than the legal limit for driving in all 50 states. 

You’ll probably feel drowsy, irritable, and may struggle to concentrate. 

Stage 2: After 36 Hours Without Sleep

A 1997 study found that 36 hours of wakefulness can reduce attention span, slow reaction time, and increase the occurrence of microsleeps — brief, involuntary episodes of unconsciousness.

Stage 3: After 48 Hours Without Sleep

Staying awake for two days straight not only makes you more prone to accidents, it also significantly weakens your immune system, as the body experiences a drop in natural killer cells that have antiviral and anti-tumor properties. Cognitive processes like decision making and judgment also take a significant hit.

Stage 4: After 72 Hours Without Sleep

If you don’t sleep for 72 hours, in addition to overwhelming sleepiness, you’ll likely experience heightened anxiety and possibly even delusions and hallucinations.

Stage 5: After 96 Hours Without Sleep 

After four days without sleep — if you can even make it this far — your grip on reality won’t be very strong. You’ll experience disordered thoughts, hallucinations, delusions, dissociation, and trouble keeping track of how much time has passed. 

There aren’t many modern studies looking at the later stages of sleep deprivation as anything beyond 72 hours is deemed unethical. So, in reality, we don’t fully know the damage these later stages would do to our brains and bodies.  

What Are the Two Types of Sleep Debt?

Because real life isn’t a timed series of extended sleep deprivation experiments, it’s helpful to use the concept of sleep debt as a way to measure and classify sleep loss. The only two stages of sleep deprivation that should really concern you are acute sleep debt and chronic sleep debt. 

Acute Sleep Debt 

Acute or short-term sleep debt is the running total of the hours of sleep you missed — as compared to your sleep need — over the past 14 days. 

Because it’s the number that best predicts how you’ll feel and function on any given day, acute sleep debt is the focus of the RISE app. We recommend keeping your sleep debt under five hours in order to feel and function at or near your best.

You don’t have to pull an all-nighter to feel the effects of sleep deprivation. For example, if you miss meeting your sleep need by just one hour per night, after 10 days you’ll be just as impaired as you would be if you’d been awake for 24 consecutive hours.

Maybe you think it’s no big deal to stay up for a couple of hours past your bedtime to watch a new movie on Netflix, but when an hour or two of lost sleep here and there starts to pile up, you’ll suffer the consequences. Acute sleep debt comes with a host of implications across every aspect of health and performance.

The Effects of Acute Sleep Debt

  • Daytime sleepiness and fatigue
  • Decreased attention span, focus, and productivity
  • A weakened immune system
  • Increased moodiness, irritability, and impatience
  • Changes to your metabolism including increased appetite
  • Increased risk of accidents

Chronic Sleep Debt

Sleep deprivation is a widespread problem with serious adverse health and social consequences, and the Centers for Disease Control and Prevention (CDC) has declared insufficient sleep a “public health epidemic.” 

Studies show that chronic sleep debt — when you go for years or decades rarely meeting your sleep need, let alone paying any of the debt back — can have serious health effects, including increased susceptibility to chronic disease and other medical conditions.

The Effects of Chronic Sleep Debt

  • Greater risk for weight gain, obesity, and type 2 diabetes 
  • Increased risk of  high blood pressure, cardiovascular disease/heart disease, and heart attack
  • Higher risk of cancers, such as colorectal cancer and breast cancer
  • More susceptible to psychiatric disorders, fertility problems, and other health problems

So, is the end state of sleep deprivation death? It certainly looks that way. Considering the serious ailments that become far more inevitable or are otherwise exacerbated by chronic sleep deprivation, it’s not surprising that years of getting less sleep than your body needs can hasten your demise. Recent research with fruit flies suggests a direct link between sleep deprivation and death.

But you don't actually have to die from sleep deprivation for it to feel like you're dying from sleep deprivation. Taking into account the extreme discomfort and cognitive decline caused by acute sleep deprivation and the serious health problems associated with chronic sleep deprivation, you might be ready to make getting enough sleep a top priority. 

But how can you know for sure if you have high sleep debt?

How Can I Tell if My Sleep Debt Is Too High?

RISE app photo showing how to keep track of your sleep debt.
The RISE app automatically calculates and keeps track of your sleep debt for you.

As humans, we’re not the best at judging whether or not we’re sleep deprived. That’s because we have a natural ability to adapt subjectively to poor sleep. After just a few nights of sleep loss, you may think you’re doing fine, but all the while, you’re actually in decline across almost every measure that matters.  

So, how do you know if you’re suffering from acute sleep debt? The RISE app will tell you. Rather than getting into the gray area of trying to define or rate so-called “sleep quality,” (sleep experts don’t have an agreed upon objective definition for sleep quality) or analyzing the different stages of sleep — deep sleep vs. rapid eye movement or REM sleep, for example — the RISE app focuses on the amount of sleep you’re getting, which is to say, whether or not you’re meeting your genetically-determined sleep need. Go further with our posts: How much deep sleep do you need? You don’t need to know and How much REM sleep do I need? PSA: You don’t need to know.

Using data from your phone, along with sleep-science-based models, the app learns your genetically driven sleep biology to calculate your sleep need in hours and minutes. From there, the app automatically calculates and keeps track of your 14-day sleep debt number for you. 

Because it’s not realistic to expect total sleep perfection all the time, we recommend keeping your sleep debt under five hours. At that level, you can still feel good and perform at or near your best. 

But what happens if your sleep debt number starts to creep up? Can you pay it down? 

Can You Pay Down Sleep Debt?

The good news is yes: you can catch up on sleep as acute sleep debt is reversible. In one study, participants who had their sleep restricted to 4.5 hours per night for a full week subsequently experienced a dramatic improvement in cognitive performance and mood after getting just two full nights of recovery sleep. 

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Unfortunately, the research on recovering from chronic or long-term sleep debt is less conclusive. According to the National Institutes of Health, scientists and sleep experts have doubts about the body’s ability to recover completely from the serious health consequences associated with chronic sleep deprivation. 

But even if you can’t totally reverse the effects of chronic sleep deprivation, making a real effort to reduce your acute sleep debt is definitely worthwhile. It doesn’t take long to start feeling the benefits of lowering your sleep debt; most RISE users feel the benefits within five days.

But if it’s possible and recommended to catch up on sleep, why do so many people believe you can’t? You might notice popular media stating you can’t recover from sleep deprivation, and there’s a few reasons for that: 

  • Confusing acute and chronic sleep debt: Articles saying you can’t catch up on sleep debt may be referring to studies on chronic sleep debt, instead of the debt you can pay back: acute sleep debt. 
  • Misunderstanding research: Even articles talking about the right type of sleep debt can get things wrong. For example, if an article says you can’t pay back sleep debt at the weekend, they may mean a one-hour lay in won’t cut it and most people won’t prioritize getting extra sleep. But that doesn’t mean you biologically can’t catch up on sleep. 
  • Misleading headlines: And, of course, we’re all aware of how headlines are written to grab our attention. A dramatic statement like “you can’t catch up on sleep” may get more clicks than one that says you can.

How Can I Reduce My Sleep Debt?

Acute Sleep Deprivation

To reverse acute sleep deprivation, you either have to outsleep your sleep need until you pay down your sleep debt or let the clock run out on the 14 days by meeting your sleep need every single night. 

Although keeping a consistent sleep schedule is an important part of a healthy sleep routine, if your sleep debt is high, making small adjustments here and there can help you get out of debt. 

You can pay down sleep debt by: 

  • Taking naps: Check RISE for the best time to do this so you don’t disturb your sleep at night
  • Going to bed a little earlier
  • Sleeping in a little later: Just be sure to keep this to one or two hours so you don't disrupt your circadian rhythm, or your internal body clock that governs your natural sleep-wake cycle and other predictable energy fluctuations in roughly 24-hour periods. 
  • Maintain excellent sleep hygiene: Sleep hygiene helps you fall asleep quicker and wake up less often during the night, therefore allowing you to get more sleep overall. More on what these sleep habits are below.

Chronic Sleep Deprivation 

If you’ve been consistently not getting enough sleep, you can still change your ways, improve how you feel, and make sure you don’t add to the problem any further. First, use RISE to work out your sleep need and start aiming to get that amount of sleep each night with excellent sleep hygiene. 

You can work out the best time to go to sleep and wake up by thinking about your sleep need, morning commitments, and your chronotype (or whether you’re a morning person or night owl. Remember to factor in some extra sleep time for sleep latency, or the time it takes to fall asleep. If you find you need to go to sleep earlier in order to get the sleep you need, you can work on resetting your sleep schedule to make that happen. 

What is Sleep Hygiene?

Sleep hygiene is the upkeep of daily and nightly behaviors that affect the way you sleep. To optimize your daily habits for a good night’s sleep and better next-day energy levels, follow these guidelines. These tips are useful for everyone, but especially for those who are trying to treat sleep deprivation. 

Time Your Light Just Right

Your circadian rhythm is heavily influenced by the sunrise-to-sunset cycle. Ideally, you want to expose yourself to light — preferably sunlight — first thing in the morning to signal your brain to stop producing melatonin, a sleep-inducing hormone. (Going for a walk or a run during your morning sun time is even better, as physical activity during the day can help you sleep better at night.) 

Be sure to get natural light throughout the day, too, as this can make you less sensitive to it at night. Work by a window, go for walks, and take your workout outside to get more natural light exposure into your day. 

In the evening, you should avoid light — especially blue light and bright light — in the 90 minutes before bed to help support and maximize your body’s melatonin production. A pair of blue-light blocking glasses can help, as can dimming the lights in your home. 

Avoid Caffeine, Alcohol, Large Meals, and Exercise Later in the Day/Night

RISE app screenshot showing you when to limit caffeine.
The RISE app can tell you when to stop sleep-disturbing behaviors each day.

Because they are known sleep disruptors, don’t consume caffeine in the 10-12 hours before bed, big meals in the three hours before bed, alcoholic beverages in the 3-4 hours before bed, and avoid exercise an hour and a half before bed. The RISE app will remind you of these cutoff times. 

Make Bedtime a Matter of Routine 

Your circadian rhythm thrives on consistency, so keep a regular bedtime and wake time that allows you to meet your sleep need. And make sure you set aside time to disconnect from the stress of the day before you go to sleep. Schedule a nightly wind-down period to do some light reading, take a warm bath or shower, meditate, or sip a cup of decaf tea.

Optimize Your Bedroom for Sleep

The perfect sleep environment is cool, dark, and quiet. Set your thermostat at 65-68 degrees, and try to keep your room completely dark. Light disrupts your body’s natural melatonin production, so use blackout curtains or blinds and an eye mask. And because ambient sounds can disturb your sleep and cause nocturnal awakenings, use a white noise machine and earplugs.

RISE can help you keep on top of 20+ sleep hygiene habits by reminding you when you should do them each day. You can learn more about how sleep hygiene can improve your sleep here.

Seek Medical Help if Needed

If you practice stellar sleep hygiene but are still suffering with sleepless nights, talk to your healthcare provider or a sleep specialist. A sleep study and other tests can help determine if an underlying medical condition, sleep apnea, restless legs syndrome, or another sleep disorder could be part of the problem. 

Measuring Sleep Deprivation Stages With Sleep Debt

Although it may be interesting to look at the effects of sleep deprivation after 24, 48, 72, and 96 hours of staying awake, breaking it down in terms of sleep debt is far more useful. After all, not many of us go 96 hours without sleep, but most of us can easily rack up sleep debt over 14 nights. 

When you know how much sleep debt you have, you know exactly how much sleep you need to get in order to keep or lower your sleep debt to less than five hours to be at your best. 

With the RISE app, all of the calculations are automatic. There are no extra steps to take to keep up with your progress. Not having to worry about or even see the fancy algorithms and all the data gathering going on behind the screen lets you focus on what’s most important — getting the right amount of sleep at night so you can have the energy you need during the day.

More on sleep deprivation and how to reverse it:

Summary FAQs

What are the five stages of sleep deprivation?

The five stages of sleep deprivation are what you experience after 24, 36, 48, 72, and 96 hours without sleep. Sleep studies often measure sleep loss in these 24-hour windows.

How long does it take to suffer from sleep deprivation?

You may start feeling symptoms of sleep deprivation after 16 hours of no sleep, and they’ll get progressively worse and more serious the longer you go without sleep. 

What are 3 common symptoms of being sleep deprived?

3 common symptoms of sleep deprivation include fatigue, irritability, and trouble concentrating.

Does sleep deprivation have stages?

Sleep deprivation symptoms are often measured in 24-hour windows, but the most applicable stages of sleep deprivation to everyday life are acute and chronic.

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