5 Reasons Why You Only Sleep a Few Hours a Night

Causes of Sleep Deprivation and Short Sleep Syndrome (SSS)

There are more than 100 different sleeping and waking disorders, and it is easy to confuse them. Sleep deprivation often occurs with sleeping disorders.

If you cannot sleep for more than four to five hours per night (or less), you may have sleep deprivation. In addition, regular sleep interruptions from things like night terrors or "sleep starts" can also lead to sleep deprivation.

If you have trouble falling asleep or staying asleep, your sleep deprivation may be caused by insomnia. But it can also be caused by other sleep disorders.

Not everyone who sleeps less than the recommended seven to nine hours per night has a sleep disorder.

For example, if you need fewer than six hours of sleep every night and don't have sleep deprivation symptoms, you likely do not have insomnia. Instead, you may have a condition known as short sleep syndrome (SSS).

This article explains the difference between sleep deprivation and SSS.

Woman watching TV in bed

iStockphoto / JGalione

Sleep Deprivation

Being unable to sleep can affect your health and well-being. Sleep disorders fall under the following categories:

  • Insomnia: Difficulty falling asleep or staying asleep
  • Hypersomnia: Excessive daytime sleepiness caused by narcolepsy, obstructive sleep apnea, and other medical conditions
  • Circadian rhythm disorders: When your biological clock is out of sync, such as in jet lag, irregular sleep-wake syndrome, and shift work syndrome
  • Parasomnias: Behaviors that interrupt your sleep, such as sleep terrors, sleepwalking, and REM sleep behavior disorder

All of these conditions can cause sleep deprivation. Often, they affect your ability to function normally as you go through your day. Symptoms of sleep deprivation include:

  • Clumsiness
  • Depression
  • Difficulty learning
  • Drowsiness
  • Fatigue
  • Forgetfulness
  • Increased carbohydrate cravings
  • Irritability
  • Less interest in sex
  • Loss of motivation
  • Moodiness
  • Trouble concentrating
  • Weight gain

Risks of Sleep Deprivation

Over time, chronic sleep deprivation can weaken your immune response, leading to infections.

It may also impact insulin production, increasing your risk for type 2 diabetes.

In addition, sleep deprivation can elevate your blood pressure, upping your risk of heart disease.


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This video has been medically reviewed by Sanja Jelic, MD

Short Sleep Syndrome

Unlike sleep deprivation, people with short sleep syndrome (SSS) regularly need fewer than six hours of sleep per night and can still function normally.

People with SSS perform well at work or school even though they have short periods of sleep. They don’t feel the need to take naps or catch up on sleep on weekends.

The cause of short sleep syndrome is not well understood. However, a 2014 study published in the journal Sleep strongly suggests that genetics play a key role.

Sleep Deprivation
  • Affects health and well-being

  • Is often caused by a sleep disorder

  • Sleep is inadequate

Short Sleep Syndrome
  • Does not cause negative symptoms

  • May be caused by a gene mutation

  • Sleep is adequate

SSS and Gene Mutations

In one study, two non-identical twins got almost identical amounts of rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. One twin had a mutation of the BHLHE41 gene and needed a few hours of sleep per night. The other didn't have the mutation and required a full night's rest to function normally.

It is thought that gene changes like this interfere with a person's sleep patterns and their drive for sleep. Usually, these kinds of sleep interferences would cause symptoms of sleep deprivation. But in people with certain gene mutations, it doesn't.

For some reason, specific changes to certain genes alter the way the brain responds to a lack of sleep. As a result, the internal clock that controls sleep is shortened without harming a person's physical or mental health.


SSS is when a person requires fewer hours of sleep, but they don't experience symptoms of sleep deprivation. Researchers have found that mutations in certain genes may be responsible for SSS.


Sleep deprivation can be caused by many different sleep disorders, including insomnia. It can cause symptoms that affect your ability to function throughout the day. For example, if you have sleep deprivation, you may have trouble concentrating, feel tired all of the time, or be crabby.

People with SSS, on the other hand, need less sleep. They do not experience negative symptoms as a result. In addition, research has found certain gene mutations in people with SSS.

A Word From Verywell

If you are not adversely affected by short sleep duration, you don't have insomnia and shouldn't be worried. Waking up refreshed after a few hours of sleep is a sign of good health, not an illness.

However, call your healthcare provider if a sleep problem lasts for more than three weeks and affects your ability to work, take care of your children, or manage daily routines. They may refer you to a sleep specialist.

Don't try to self-diagnose and self-treat what you assume to be insomnia. In some cases, poor sleep patterns may be a sign of a serious medical condition requiring specific treatment and care.

Frequently Asked Questions

  • Is it bad to only get six hours of sleep?

    Not always, though it's less than the general recommendation of seven to nine hours per night. Some people can get by just fine with six hours of sleep each night, while others may need up to eight or nine hours. Sleep needs can be influenced by certain factors like genetics, age, overall health, and amount of daily activity.

  • Why can't I stay asleep through the night?

    There are many reasons why people have trouble staying asleep at night. Common reasons include the following:

    • Stress
    • Poor sleep environment caused by loud noises or light
    • Too much caffeine
    • Back pain
    • Shifting hormones
    • Drinking alcohol before sleep
    • Eating before sleeping
  • What is short sleep syndrome?

    Short sleep syndrome describes people who can function normally with less than six hours of sleep each night. It is believed to be genetic.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Medic G, Wille M, Hemels ME. Short- and long-term health consequences of sleep disruption. Nat Sci Sleep. 2017;9:151-161. doi:10.2147/NSS.S134864

  2. Pellegrino R, Kavakli I, Goel N et al. A novel BHLHE41 variant is associated with short sleep and resistance to sleep deprivation in humans. Sleep. 2014;37(8):1327-1336. doi:10.5665/sleep.3924

  3. American Sleep Association (ASA). 7 reasons why you can't stay asleep.

  4. University of California, San Francisco (UCSF). After 10-year search, scientists find second 'short-sleep' gene.

By Brandon Peters, MD
Brandon Peters, MD, is a board-certified neurologist and sleep medicine specialist.