Exhaustion and sleep loss may have negative consequences, such as mood changes, slower reaction time, and hallucinations. In rare cases, it may be life threatening.

Suffering through one sleepless night after another can make you feel pretty rotten. You might toss and turn, unable to get comfortable, or simply lie awake while your brain wanders restlessly from one anxious thought to another.

Exhaustion and sleep loss can have plenty of consequences, but it’s pretty rare to die from lack of sleep. That said, operating on little to no sleep can increase your risk of having an accident while driving or doing something potentially hazardous.

Getting less sleep than you need for a night or two can lead to a foggy, unproductive day, but it usually won’t hurt you much.

But when you regularly lose sleep, you’ll start to see some unwanted health effects pretty quickly. Consistently getting just an hour or two less sleep than you need can contribute to:

  • slower reaction time
  • changes in mood
  • higher risk for physical illness
  • worsened mental health symptoms

What about going an entire night without sleep? Or longer?

You’ve probably pulled an all-nighter or two before. Maybe you stayed up all night to put the finishing touches on a budget proposal or complete your graduate thesis.

If you’re a parent, you may have experienced more than a few sleepless nights — and you probably have a few choice words about the myth that coping with lost sleep gets easier over time.

Your body needs sleep to function, and going without doesn’t just feel unpleasant, it can also have some pretty serious consequences.

Missing just one night of sleep may not be too problematic, but you’ll start to notice some side effects. The longer you go without, the more severe these effects will become.

Here’s how the body tends to respond when you stay awake for:

1 day

Staying awake for 24 hours can affect you in much the same way as intoxication.

Research from 2010 suggests that staying up for 20 to 25 hours affects your focus and performance as much as having a blood alcohol level (BAC) of 0.10 percent. In most places, you’re considered to be legally drunk when you have a BAC of 0.08 percent.

Needless to say, you’re going to want to avoid driving or doing something potentially unsafe if you’ve been up for a full day and night.

A sleepless night can have other effects, too.

You might notice things like:

  • daytime sleepiness
  • fogginess
  • changes in mood, like crankiness or a shorter temper than usual
  • difficulty concentrating or making decisions
  • tremors, shakiness, or tense muscles
  • trouble seeing or hearing

1.5 days

After 36 hours without sleep, you’ll begin noticing a much heavier impact on health and function.

Prolonged disruption of your normal sleep-wake cycle puts your body under stress. In response, it ramps up the production of cortisol (the stress hormone).

Hormonal imbalances can affect your body’s typical reactions and functions. You might notice changes in your mood and appetite, increased stress, or chills and other changes in your body temperature.

Your body’s oxygen intake can also decrease when you stay awake for this length of time.

Other consequences of 36 hours of sleeplessness include:

  • patchy memory
  • declining energy and motivation
  • short attention span or inability to pay attention
  • cognitive difficulties, including trouble with reasoning or decision-making
  • intense fatigue and drowsiness
  • trouble speaking clearly or finding the right word

2 days

When you go without sleep for 48 hours, things start to get pretty miserable. You may drift through the day, feeling foggy or completely out of touch with what’s happening.

General effects of sleep deprivation usually worsen. You might find it even more difficult to concentrate or remember things. You might also notice increases in irritability or moodiness.

The effects of sleeplessness on your immune system also intensify after 2 days. This can increase your chances of getting sick since your immune system can’t fight off illness as well as it usually would.

Staying awake also becomes pretty challenging.

After 2 full days without sleep, people often begin experiencing what’s known as a microsleep. A microsleep happens when you lose consciousness briefly, for anywhere from a few seconds to half a minute. You don’t realize what’s happening until you come to, but you’ll probably reawaken with some confusion and grogginess.

3 days

If you’ve gone 3 days without sleeping, things are about to get weird.

Chances are, you won’t be able to think about much besides sleep. You’ll probably find it difficult to focus on conversations, your work, even your own thoughts. Even simple activities, like getting up to look for something, might seem too difficult to contemplate.

Along with this extreme exhaustion, you might notice your heart is beating much more rapidly than usual.

You’ll probably also notice changes in mood or problems with emotional regulation. It’s not uncommon to experience feelings of depression, anxiety, or paranoia after going without sleep for a few days.

Going without sleep for this length of time can also affect your perception of reality, which can:

  • cause illusions and hallucinations
  • make you believe inaccurate information is true
  • trigger what’s called the hat phenomenon, which happens when you feel pressure around your head

More than 3 days

To put it plainly, going without sleep for 3 days or longer is very dangerous.

The side effects listed above will only get worse. You’ll probably start experiencing more frequent hallucinations and increased paranoia. Eventually, symptoms of psychosis can trigger a disconnect from reality.

Your risk of having an accident while driving or performing any potentially risky task will increase greatly as you experience more microsleeps. If it’s been more than 3 days and you can’t sleep, it’s best to see your healthcare provider right away.

Eventually, your brain will begin to stop functioning properly, which can lead to organ failure and, in rare cases, death. Plus, your risk of having some kind of accident skyrockets.

So far, we’ve established two things: Sleep is essential, and going without sleep can eventually cause some pretty nasty side effects.

But it may surprise you to learn you actually can have too much of a good thing. While sleeping too much usually isn’t life threatening, it’s been associated with a higher mortality rate.

Chronic oversleeping can also cause:

  • cognitive impairment, including problems with reasoning and speaking
  • daytime drowsiness
  • sluggishness or low energy
  • headaches
  • feelings of depression or low mood
  • trouble falling or staying asleep

A 2014 study of 24,671 adults found evidence to link sleeping more than 10 hours a night, or long sleeping, to depression and obesity. Long sleeping has also been associated with high blood pressure and type 2 diabetes.

Experts have developed some recommendations to help you determine just how much sleep you need. Getting close to this amount most nights can prevent side effects of sleep deprivation and help you maintain good health overall.

Most adults need between 7 and 9 hours of sleep per night. Your optimal sleep time may depend on a few factors, including age and gender. Older adults may sleep a little less, and women may sleep a little more.

Check out our sleep calculator to get a better idea of how much sleep you need each night.

If you regularly have problems getting enough restful sleep, it may help to take a look at your sleep habits.

These tips can help you get more — and better — sleep:

Only use your bedroom for sleep

Your bedroom should be a sacred place. Limiting bedroom activities to sleeping, sex, and maybe a little reading before bed can help you switch to relaxation mode when you enter your room. This helps you prepare for sleep.

Avoid working, using your phone, or watching TV in your bedroom, as these can wake you right back up.

Make your bedroom as comfortable as you can

A soothing sleeping environment can help you get to sleep more easily. Follow these tips:

  • Keep your room cool to sleep better.
  • Layer your blankets so they can be easily removed and added back if needed.
  • Choose a comfortable mattress and pillows, but avoid cluttering the bed with pillows.
  • Hang curtains or light-canceling blinds in order to block light.
  • Use a fan for white noise if you live in an apartment or have noisy roommates.
  • Invest in quality sheets and blankets.

Consistency is key

You might not need to go to bed early on the weekends, or any other time when you don’t have to get up at a specific time, but getting up at odd hours can throw off your internal clock.

If you stay up late one night and still have to get up early, you might plan to catch up with a nap. This sometimes helps, but napping can complicate things even more: Take a nap too late in the day, and you won’t be able to get to sleep on time that night, either.

To get the best sleep, try going to bed around the same time every night and getting up at approximately the same time each morning, even if you don’t have to.

Activity can help

Physical activity can tire you out, so it might seem logical to assume getting enough exercise will improve your sleep.

It certainly can. Better sleep is among the many benefits of regular physical activity. If you’re having trouble sleeping, though, make sure to get that workout in at least a few hours before bedtime.

Exercising too late in the day can wear you out and keep you awake.

Looking for more tips? Here are 17 more to help you get to bed (and stay there).

Missing a night or two of sleep won’t kill you, but it can do a number on your health and ability to function during the day.

Because good sleep is such an important part of good health, it’s wise to talk to your healthcare provider if you continue to have trouble sleeping, whether that trouble involves too little sleep or too much.

Crystal Raypole has previously worked as a writer and editor for GoodTherapy. Her fields of interest include Asian languages and literature, Japanese translation, cooking, natural sciences, sex positivity, and mental health. In particular, she’s committed to helping decrease stigma around mental health issues.