What happens to your body if you don't sleep?

Just one sleepless night is enough to leave you feeling tired and sluggish, wanting only to sit on the sofa and feeling more irritable than able to get anything done. So what happens to your body if you go without sleep for days on end?

 

Many people divide sleep deprivation into five stages, based on how long a person stays awake. The first stage, when a person stays awake for 24 hours straight without sleep, doesn't sound too bad, but it's not ideal either. If you've ever stayed up all night or had to stay awake with a fussy newborn, you know the misery of just one night of sleep deprivation. Besides exhaustion and stress, you're more likely to make mistakes throughout the day, as concentration and overall cognitive abilities are severely affected by about eight hours of sleep deprivation.

After 24 hours without sleep, hallucinations may appear… and may get worse.

Hallucinations can begin as early as 24 hours without sleep. They may manifest as relatively mild changes in perception, but as time goes on without sleep, they can turn into more vivid images, potentially even leading to psychosis.

 

What's the cause? Numerous studies suggest dopamine plays a crucial role. This neurotransmitter regulates many bodily functions, including memory, mood, and motivation. When it comes to sleep, dopamine appears to be involved in the rapid eye movement (REM) sleep phase, where you're most likely to dream and process information learned during the day. Staying up too late can disrupt dopamine levels; scientists have found that too much dopamine in certain brain regions is linked to auditory hallucinations in animal studies (according to Science). Oddly, Tripp's hallucinations seem to occur in cycles mimicking REM sleep phases.

Your body will try to force you to sleep.

Willpower can be a great help, but when it comes to fighting sleepiness, your body is working hard to gain the upper hand in order to rest. People who stay up late for extended periods, whether they choose to or not, are fighting against a series of their own body's efforts to get them to sleep. Generally, after about 36 hours, you'll feel an intense urge to sleep as your body's sleep pressure builds. This pressure will continue to increase until many people simply drift off to sleep involuntarily.

But they may not actually know they've fallen asleep. In some cases, people may experience extremely brief periods of unconsciousness called somnolence. These last only a few seconds.

 

Severe cognitive decline can result from prolonged sleep deprivation.

If you've ever completely missed a night's sleep, you know that thinking afterward can be frustratingly slow. But prolonged sleep deprivation can lead to more problems than just having to reread instructions or taking the wrong route. A 2003 study published in the journal Sleep tracked 48 adults, divided into three groups with sleep time restricted to eight, six, or four hours each night for 14 days.

Participants in the four-hour sleep group experienced a significant decline in alertness, working memory, and overall cognitive ability. Researchers found that those who slept six hours or less began experiencing similar cognitive problems to those who stayed up for two consecutive nights.

So what cognitive issues are we talking about? A 2025 review published in the journal Military Medicine found that most studies examining test subjects based on reaction time and accuracy of responses, some focusing on short-term working memory. Other factors included the ability to switch between tasks efficiently, motivation, and emotional state. All were affected to some degree, although some factors (like attention and reaction time) improved if subjects had adequate sleep beforehand—but only for a short time.

The ability to make socio-emotional judgments and accept risks becomes disordered.

Numerous other studies have shown that sleep deprivation is more likely to increase risky behavior. This is particularly concerning for parents of teenagers who are already at risk, and who themselves – perhaps not coincidentally – are often sleep-deprived.

Internal organs become weak and unhealthy over time.

Your body needs sleep – that's right, your whole body. Lack of sleep can wreak havoc on your metabolism and is linked to an increased risk of obesity and type 2 diabetes. And if you've ever experienced sleep deprivation, even for a short time, and its impact on your mood, it's no surprise that mental health can be severely affected by a lack of good sleep.

In short, most of your internal organs can be damaged by severe and prolonged sleep deprivation.