What Happens to You When You Don’t Sleep for Days

All-night study sessions, important business deals, new babies — most people will experience a taste of sleep deprivation at some point in life. While an occasional lack of sleep may not seem like a big deal, its impact can be intense and its effects can linger. And if you make it a habit, not sleeping enough can have severe consequences on your health.

“As a society, as families and individuals, we have not yet fully appreciated the importance of sleep,” says Terry Cralle, RN, a certified clinical sleep educator based in Fairfax, Virginia. “Sleep, along with diet and exercise, constitutes the very foundation of good health.”

They’re so interconnected that each of them needs to be a priority, she adds.

Chronic poor sleep puts us at increased risk of serious medical conditions, such as obesity, heart disease, and diabetes. During sleep, the body secretes hormones that help control appetite, metabolism, and glucose processing. Poor sleep can lead to an increase in the body’s production of cortisol, also known as the stress hormone. In addition, skimping on sleep seems to throw other hormones out of whack. Less insulin is released after you eat, and that, along with the increased cortisol, may lead to too much glucose in the bloodstream and thus an increased risk of type 2 diabetes.

Everyone is different, but according to the Centers for Disease Control and Prevention, adults should get between seven and nine hours of sleep each night. And contrary to popular belief, sleeping an extra hour or two on the weekends cannot make up for the lost sleep you may have experienced over the course of a busy week. It could also throw off your internal body clock and possibly lead to insomnia on Sunday night. Sticking to a consistent sleep schedule is the best way to regulate the body’s clock.

Here’s what happens to the body when you miss out on shut-eye.

After 24 hours of no sleep, stress hormones — specifically cortisol and adrenaline — increase to compensate for the fatigue we’re battling and to help us keep functioning, explains John Cline, PhD, an assistant professor of clinical psychology at the Yale School of Medicine and fellow of the American Academy of Sleep Medicine.

“The brain is trying to cope with not having its opportunity to rejuvenate itself, so we have these heightened stress hormones to keep the body activated,” Dr. Cline says.

The consequences of sleep deprivation at 24 hours are comparable to the cognitive impairment of someone with a blood alcohol content of 0.1 percent, according to past research. You have a reduced reaction time, slurred speech, and slowed thinking, says the Cleveland Clinic. (For reference, in most states, the alcohol limit to legally drive is 0.08 percent.)

That level of cognitive impairment could be enough to spell danger, depending on what you’re doing.

Cline points to research that suggests people have an increased risk of car accidents after working an overnight shift, because of drowsiness.

In a small study published in the Journal of Sleep Research in 2016, 29 healthy young men were kept awake for 24 hours, and it was found that the lack of sleep made them more likely to recall false memories.

“Judgment is affected, memory is impaired, and there’s deterioration in decision-making ability and eye-hand coordination,” Cralle says. You also tend to be more emotionally reactive, attention is decreased, hearing is impaired, and there is an increase in your risk of death from a fatal accident, she says.

Now your health begins to be at risk. High levels of inflammatory markers are in the bloodstream, which can eventually lead to cardiovascular disease and high blood pressure, Cralle explains. During a typical healthy night of sleep, blood pressure drops by around 10 to 20 percent. (According to Mayo Clinic, blood pressure dropping less than 10 percent overnight is a sign of an irregular blood pressure pattern.) But if sleep is chronically interrupted or not happening at all, remaining at an elevated blood pressure may be a risk factor for hypertension, research suggests.

Additionally, hormones are affected — which means your emotions can be all over the place. As your body keeps pumping cortisol into your bloodstream, raising your heart rate and blood pressure to keep you alert, the continued stress can increase feelings of anxiety and mood swings, Cline says.

If you were cranky, on edge, and zombie-like before, those symptoms will likely worsen after 36 hours with no sleep, Cline says. “Everything going on at 24 hours is going to be worse at 36 hours.”

Cognitive impairment gets much more severe as well. You’ll likely feel sluggish and experience delayed reaction time, foggy memory, and an inability to concentrate, learn new information, and process social cues, says Michelle Drerup, PsyD, a psychologist and director of the Behavioral Sleep Medicine Program at the Cleveland Clinic.

Another study, which kept 35 undergraduate students awake for 36 hours, found that the group was slow to notice changes in their environment and had a delayed response to new stimuli in their surroundings.

Dr. Drerup says that at the 48-hour mark, you’re dealing with “extreme sleep deprivation.”

The body begins to compensate by shutting down for “microsleeps” — 3- to 15-second bursts of rest — during which your brain switches off, Drerup says. Your eyes don’t necessarily close, and you may not be consciously aware of what’s occurring, but your brain is going offline for seconds at a time.

Brain waves measured by electroencephalogram suggest that during microsleep there are both differences and similarities to the four stages of sleep, according to research.

After two days of no sleep, you can count on increased irritability, anxiety, foggy memory, and impaired thinking, says Hussam Al-Sharif, MD, a pulmonologist and sleep medicine specialist at the Mayo Clinic in Eau Claire, Wisconsin.

Some people may even encounter hallucinations — seeing or hearing things that aren’t really there. “Some people feel depressed, and some might become euphoric,” Dr. Al-Sharif adds.

Research suggests that the immune system takes a hit, too. In a study of 16 volunteers who had to forgo sleep for 72 hours, researchers found that NK cells — or natural killer cells — decreased by 37 percent after 48 hours of wakefulness. NK cells play a key role in fighting off viruses and tumor formation.

Expect significant deficits in concentration, motivation, perception, and other higher mental processes after many sleepless hours, Cralle says.

A study published in Comprehensive Psychiatry studied 12 astronauts who were assigned to isolation for 72 hours or sleep deprivation for 72 hours. The group that had to stay awake for three days had increased heart rates, higher negative mood, and lower positive emotions, compared with the group that had to live in solitude for three days.

You’re going to feel pretty miserable and dysfunctional with this much sleep deprivation, Cline says. “The brain is fighting against wanting to shut down, and that’s going to create a really fragile emotional state.”

Microsleeps also increase in length and frequency.

Cline says that this is a protective response by the body — but those fleeting moments of involuntary rest are incredibly risky, especially if you’re behind the wheel, operating heavy equipment, or responsible for make-or-break decisions at work.

This is also when the mind is ripe for hallucinations, delusions, and paranoia, Al-Sharif says.