Sleep impacts both mental health and physical health.
Many factors affect sleep quality and sleep quantity, and insufficient sleep leads to a variety of health problems.
How much sleep you need varies by age and lifestyle, but generally, adults need 7-9 hours of sleep each night.
In controlled sleep studies, participants who stayed awake for eight to 10 days showed substantial cognitive deficits.
Imagine this scenario: You’re tired, but you’ve got a lot to do, so you go to bed later than you should. When your head finally hits the pillow, you can’t shut off your mind. You’re ruminating on some thorny issues. You’re mentally making tomorrow’s to-do list. You’re worrying about things you can’t control. Sometimes you’re not worrying at all—but your mind flits from one random thought to another. Before you realize it, morning comes, the alarm goes off, and you haven’t slept at all. Yikes!
While failing to get enough sleep will certainly slow you down mentally and physically the rest of the day, it also negatively affects your health in a variety of ways. And many factors—from stress and illness to poor eating habits and medications—can be a barrier to a good night’s sleep. 
An occasional sleepless night is normal, and some people struggle with more serious, ongoing sleep problems. What happens if you don’t sleep at all? Read on to learn more about the effects of inadequate sleep.
How Much Sleep Do You Actually Need?
Just like eating, drinking, and breathing, sleep serves an essential function. In fact, humans can survive longer without food or water than without sleep. 
It helps to understand the 24-hour sleep/wake cycle (called the circadian rhythm). This internal body clock helps determine when you fall asleep and wake up. As part of this cycle, the body produces melatonin—the hormone that promotes sleep—which increases as it gets darker and decreases as it gets lighter. This sleep cycle goes through four stages that include dozing off and subdued stages, deep sleep, and REM sleep. Truly restorative sleep (your goal!) involves moving smoothly from one sleep cycle stage to the next. Generally, you progress through four to six rounds of sleep cycle every night. 
So, getting sufficient sleep means you need quality sleep at the right time in the right quantity to allow your body and mind to recharge.
Is there a precise number of hours of sleep you need each night to get that rest-and-refreshed feeling? While there’s not one “magic number,” you can follow some general guidelines to ensure you are getting sufficient sleep. Also, know that the amount of sleep you need changes as you age. Experts at the National Sleep Foundation recommend following these daily guidelines for how much adequate sleep you need. 
By practicing healthy sleep habits (a.k.a. sleep hygiene), you can stave off sleep deprivation and get the above recommended slumber each night. In a nutshell, good sleep hygiene means adopting lifestyle habits that promote quality shuteye to keep your sleep schedule on track. Examples include sticking to a consistent sleep schedule, establishing a consistent bedtime routine, watching what you eat (and when), and limiting screen time near bedtime.
Is Not Getting Enough Sleep Unhealthy?
While an occasional bad night’s sleep will make you feel irritable and tired the next day, frequent inadequate sleep can wreak havoc on your health. Energy supplements to help support cellular energy production such as B vitamins, magnesium, or CoQ10 might be helpful for those that want to help support the body's energy processes but often don't make up for poor sleep. What happens if you don’t get enough sleep? Poor sleep can cause both mental and physical health issues. Research shows that sleep deprivation can lead to both health problems, such as: [5,6,7,8]
Lack of alertness
Excessive daytime sleepiness
Slower physical and mental reaction time
Difficulty with decision-making and problem-solving
Some people think they can “get by” on less sleep—perhaps clocking in just four or five hours a night—with no negative effects. However, these “short sleepers” are only shortchanging themselves. Research shows that getting adequate quality sleep is essential for mental health, physical health, safety, and quality of life. 
If you’re getting six hours of sleep or less each night, this increases your risk for Obesity by 21 percent along with other health problems. 
Eventually, that sleep loss adds up and can be a cause for concern. In fact, if you regularly choose to sleep less than what you need, that total lost sleep is known as your sleep debt. (The same holds true if you experience involuntary sleep loss.). For example, if you lose two hours of sleep each night for a week, your sleep debt will total 14 hours after seven days. 
But what happens if you don’t sleep at all? You may have pulled an all-nighter at some point—then struggled to function at your normal capacity the next day. But one high school student conducted a sleep study for a science fair in 1965 and stayed awake for 264 hours (about 11 days) which set an apparent world-record for the science fair.  And in other carefully monitored sleep studies, participants stayed awake for eight to 10 days. While they showed no serious medical, neurological, physiological, or psychiatric issues (and they recovered after one to two nights of sleep) all of them showed substantial cognitive deficits as sleep deprivation increased, including difficulties in concentration, motivation, and perception. 
According to one study published in the International Journal of Occupational Medicine and Environmental Health, humans can survive several days of continuous sleep deprivation, but our wellbeing and effectiveness deteriorates. Furthermore, the study found that just 20-25 hours of sleeplessness impairs cognitive functioning on par with someone with a blood alcohol level of 0.10 percent. 
For an anecdotal look into how total sleep deprivation affects the body and mind, Army veteran Scott Kelley shared his experiences on the battlefield, noting these effects after staying awake more than 24 hours. 
At 48 hours: body shuts down for microsleeps (similar to short “blackouts”), followed by periods of disorientation,
At 72 hours: major cognitive decline in concentration, motivation, and perception; hallucinations
To return to the original question, “How long can a person go without going to sleep?” the final answer remains unclear. What is clear? Sleep is as necessary as food and water to survive. And the more sleep deprived you become, the greater its toll on the healthy functioning of your body and mind.
The Bottom Line
What happens if you don’t get enough sleep? In carefully monitored sleep studies, participants who stayed awake for eight to 10 days showed substantial cognitive deficits as sleep deprivation increased, including difficulties in concentration, motivation, and perception.
Lack of sufficient sleep affects your mental and physical health. The longer you go without sleep, the greater the impact, as sleep deprivation can lead to serious health problems.
Lisa Beach is a seasoned journalist whose work has been published in The New York Times, Good Housekeeping, Eating Well, Parents, AARP’s Disrupt Aging, Optimum Wellness, and dozens more. She also writes for a variety of health/wellness-focused brands. Check out her writer’s website at www.LisaBeachWrites.com.
Senior Manager, Medical and Scientific Communications
Melissa is a Registered Dietitian and provides leadership to Pharmavite’s Medical and Scientific Education team. She has over 20 years of experience educating consumers, healthcare professionals, retailers and employees about nutrition, dietary supplements, and overall wellness. Prior to joining the Medical and Scientific Communications team, Melissa launched and managed Pharmavite’s Consumer Affairs department and worked as a clinical dietitian throughout Southern California. Melissa received her Bachelor of Science degree in Nutritional Sciences from the University of Arizona in Tucson, Arizona, and completed her dietetic internship at Veteran’s Hospital in East Orange New Jersey.