Sleep Disorders: Overview

A sleep disorder is a medical disorder in which the pattern, timing, or restfulness of a person's sleep is disturbed. Sleep disorders may be either primary (occurring on their own) or secondary (caused by another medical or psychiatric condition).

Did You Know?

Why Are Sleep Disorders Important?

When people do not get a normal amount of refreshing sleep, they are not at their best. They may be impatient or careless, or they may show poor judgment in their actions. They may also be irritable with family and friends. Sleeplessness can cause serious accidents, as when someone “nods off” while driving a car or operating machinery.

An estimated 40 million Americans have serious sleep problems that can be damaging to their health, and about a third of all American adults will have a sleep disorder at some point in life. The estimated cost to U.S. employers in lost productivity due to sleep loss issues is 18 billion dollars a year.

In order to understand sleep disorders, it is necessary to understand basic information about sleep itself and the wide range of normal variations in the way people sleep.

What Is Normal Sleep?

On average, about one-third of a person's life is spent sleeping, but the amount and timing of sleep vary considerably in different people, based on their age and lifestyle. Newborn infants may sleep up to 20 hours per day. Young and middle-aged adults sleep about eight hours on average. Elderly people tend to get less sleep at night but may take naps during the day.

Recommended Hours of Sleep by Age The National Sleep Foundation (NSF) issued new recommendations for appropriate sleep durations in 2015, including recommendations for minimum and maximum hours of sleep.

Recommended Hours of Sleep by Age The National Sleep Foundation (NSF) issued new recommendations for appropriate sleep durations in 2015, including recommendations for minimum and maximum hours of sleep.
SOURCE: (accessed March 31, 2016). Table by Cenveo Publisher Services. © 2016 Cengage Learning®.

Percentage of U.S. high school students who had 8 or more hours of sleep,* by sex, race/ethnicity, and grade, 2013

Percentage of U.S. high school students who had 8 or more hours of sleep,* by sex, race/ethnicity, and grade, 2013
SOURCE: Centers for Disease Control and Prevention (CDC). Youth Risk Behavior Surveillance—United States, 2013. MMWR 2014; 63 (No. SS-4): 166. Table by Lumina Datamatics Ltd. © 2016 Cengage Learning®.

What Are the Types and the Stages of Sleep?

Scientists at sleep laboratories have discovered that there are two distinct types of sleep. One is called rapid eye movement or REM sleep because the eyes can be seen moving rapidly beneath the closed eyelids. Dreaming takes place during REM sleep, and the brain waves of someone in REM sleep look much like those of a person who is awake when the waves are measured on an electroencephalogram (EEG) * .

The other type, non-REM sleep, consists of four stages in which the brain waves become progressively deeper and slower but then speed up again until the REM stage occurs. This cycle is normally repeated with some variation at approximately 90-minute intervals, with REM sleep usually taking up about 25 percent of the total.

Studies conducted in sleep laboratories have contributed greatly to the diagnosis and treatment of sleep problems.

Types of Sleep Disorders

Sleep disorders include insomnia, sleep apnea, narcolepsy, hypersomnia, restless leg syndrome, and situational sleep loss. Night terrors and sleepwalking are also considered sleep disorders.


Insomnia (in-SOM-nee-uh) is a general term for trouble with sleeping (the English word comes from the Latin somnus, which means sleep). People with insomnia may have difficulty falling asleep, or they may wake up too early in the morning. Some wake up frequently during the night and then find it hard to go back to sleep.


One of the symptoms of sleep apnea is snoring; however, snoring can have other causes, including alcohol consumption, sedative medication use, chronic nasal congestion, or obstruction caused by enlarged adenoids * and tonsils * .

In most cases, medical professionals do not know what causes snoring: some people just snore. Sometimes, however, they can find a cause. If a patient's snoring is punctuated by extended quiet periods before snoring resumes, a doctor may identify the snoring as a symptom of sleep apnea and then suggest treatment options. Treatment options range from quitting smoking and losing weight to dental appliances, sleeping on special orthopedic pillows, or surgery.

Sleep apnea

A person with sleep apnea (AP-nee-a) stops breathing intermittently for periods of about 10 seconds or more while asleep. The most common and severe type is obstructive sleep apnea (OSA). In this disorder, the muscles at the back of the throat relax and sag during sleep until they obstruct the airway. The pressure to breathe builds up until the sleeper gasps for air. Central sleep apnea is another type of sleep apnea that occurs when the brain temporarily “forgets” to tell the body to breathe. Mixed apnea is a combination of OSA and central sleep apnea. These episodes may occur hundreds of times a night and are accompanied by awakenings so brief that the affected person usually does not remember them. People with sleep apnea typically complain of being very tired during the day. Severe sleep apnea can induce high blood pressure and increase the risk of stroke * , heart attack, and even heart failure.

Sleep apnea can affect people of all ages, but it is most common in older individuals. OSA occurs most often in men who are 50 or older, and many people with OSA are overweight. People with sleep apnea often do not know that they have the condition. Family members are well aware of the problem because the most common symptom of sleep apnea is loud snoring.


Like sleep apnea, narcolepsy (NAR-ko-lep-see), involves excessive daytime sleepiness. In narcolepsy the person cannot resist falling asleep. Some people with narcolepsy also experience frightening hallucinations * or sleep paralysis * , which is an inability to move or speak while falling asleep or waking up.

Research has shown that during a sleep attack, the REM stage of sleep intrudes suddenly into the waking state. Narcolepsy is a lifelong condition of unknown cause that runs in families. Sometimes socially embarrassing or inconvenient, this disorder can also be severely disabling and lead to injury.


People with hypersomnia may sleep for excessively long periods during the day or longer than normal at night. Drowsiness or sleep periods last longer than with narcolepsy. Psychological depression * is often the main cause.

Restless leg syndrome

Restless leg syndrome is characterized by frequent leg movements due to discomfort inside the legs, usually aching or prickling sensations that prevent affected persons from falling asleep. In some individuals, sleep is then disrupted by involuntary leg jerking, which in some women is more troublesome during pregnancy.

Situational sleep loss

Situational sleep loss (also known as situational insomnia) occurs as a result of a stressful event, such as a family crisis, workplace problems, or financial issues. When the worries surrounding the specific event are resolved, the insomnia usually dissipates as well. Patients with situational sleep loss may benefit from relaxation techniques and/or pharmacologic treatment options from their physician, counselor, or therapist.


While many Americans are sleep-deprived due to a long-known sleep disorder like insomnia, sleep apnea, or narcolepsy, many more do not get enough sleep because of modern technology–specifically, the widespread availability and popularity of portable electronic devices like smartphones and tablets as well as desktop and laptop computers. These devices make it increasingly difficult for people to “wind down” before bed and get enough sleep. Teenagers and college students are often tempted to stay up late interacting on social media, playing video games, or enjoying the 24/7 entertainment available on television or the Internet, while their parents may work in occupations in which they are expected to be available to employers or clients at all hours. The statistics of evening and late-night use of electronic devices are startling, according to the annual Sleep in America poll conducted by the National Sleep Foundation (NSF):

To encourage longer and more restful sleep, the NSF recommends limiting the use of electronic devices before bed:

Nightmares, night terrors, and sleepwalking

Almost everyone has nightmares occasionally. These unpleasant vivid dreams occur during REM sleep, usually in the middle or late hours of the night. Upon awakening, the dreamer often remembers the nightmare clearly and may feel anxious. Nightmares are especially common in young children. In adults, they may be a side effect of certain drugs or of accidents, natural disasters, or other traumatic events.

Sleep apnea patient using a continuous positive airway pressure (CPAP) machine. CPAP is a treatment that uses mild air pressure to keep the airway open. CPAP typically is used by people who have sleep apnea or other breathing problems.

Sleep apnea patient using a continuous positive airway pressure (CPAP) machine. CPAP is a treatment that uses mild air pressure to keep the airway open. CPAP typically is used by people who have sleep apnea or other breathing problems.

A night terror is quite different from a nightmare and is much less common, affecting between 1 percent and 6 percent of children and less than 1 percent of adults. It occurs in children during deep non-REM sleep, usually an hour or two after going to bed. During an episode, they may sit up in bed shrieking and thrashing about with their eyes wide open. Typically, the next day they remember nothing of the event. Night terrors occur chiefly in preschool children. Although frightening, night terrors generally are harmless and children soon outgrow them.

Sleepwalking also occurs during non-REM sleep. It was once believed to be a reenactment of dreams, but such is not the case. Sleepwalking takes place most commonly in children. The sleepwalker wanders about aimlessly, appearing dazed and uncoordinated, and remembers nothing of the episode afterward.

How Do Doctors Diagnose and Treat Sleep Disorders?

Most sleep disorders can be treated successfully if diagnosed properly. Anyone who sleeps poorly for more than a month or has daytime sleepiness that interferes with normal activities may wish to consult a doctor or be referred to a specialist in sleep disorders.

At a sleep clinic, patients are first asked questions about their medical history and sleep history. A polysomnogram (POL-ee-SOM-no-gram) is sometimes used to measure brain waves, muscle activity, breathing, blood oxygen * level, and other body functions during sleep.

Many sleep disorders, such as jet lag, short-term insomnia, and most nightmares, do not need treatment. Some others, such as night terrors, are outgrown.

Chronic insomnia often is treated successfully with behavior therapy, which involves various relaxation techniques and reconditioning to change poor sleeping habits. Sleeping pills may be used temporarily, but their long-term use is controversial due to unwanted side effects, including their potential to be habit-forming.

Obstructive sleep apnea is often treated with dental appliances or one of two devices: continuous positive airway pressure (CPAP) or bi-level positive airway pressure (BiPAP). These devices keep the airway open. Operations to widen the area at the back of the throat or to provide a new opening into the windpipe below the Adam's apple sometimes are performed to treat severe obstructive sleep apnea.

For restless leg syndrome, people can alter their routines, incorporating stretching, walking, and regular exercise into their daily patterns. Massage may also be helpful. If the problem requires medical treatment, physicians can prescribe various types of drugs; for example, a dopamine agonist like ropinirole (Requip) or a sedative like zolpidem (Ambien).

Hypersomnia due to depression is often helped by psychotherapy * .

There is no cure for narcolepsy and restless leg syndrome, but medications can help control or ease symptoms.

How Can Sleep Disorders Be Prevented?

Most sleep disorders can be prevented or minimized by making a few lifestyle changes. Some simple guidelines include:

See also Anxiety and Anxiety Disorders: Overview • Caffeine-Related Disorders • Depressive Disorders: Overview • Insomnia • Jet Lag • Narcolepsy • Stress and Stress-Related Illness


Some over-the-counter sleep aids contain melatonin (MELL-a-TO-nin). Melatonin is a hormone secreted during the hours of darkness by the pineal (PIN-e-al) gland, a small structure located over the brain stem (the part of the brain connected directly to the spinal cord that controls such basic functions of life as breathing and blood pressure).

Melatonin appears to be part of the system that regulates sleep-wake cycles in humans. Some research studies have shown that a small dose of melatonin at night helps make falling asleep easier, and that melatonin may be beneficial to travelers who have jet lag.

Melatonin is available for sale without a prescription, but the Food and Drug Administration does not regulate its production or sale. Studies of this product to determine whether melatonin is safe for use were ongoing as of 2016.


Books and Articles

Rosenberg, Robert. Sleep Soundly Every Night, Feel Fantastic Every Day: A Doctor's Guide to Solving Your Sleep Problems. New York: Demos Medical Publishing, 2014.

Wilson, Sue and David Nutt. Sleep Disorders. 2nd ed. Oxford, UK: Oxford University Press, 2013.


Centers for Disease Control and Prevention. “Sleep and Sleep Disorders.” (accessed July 10, 2016).

MedlinePlus. “Insomnia.” U.S. National Library of Medicine, National Institutes of Health. (accessed July 10, 2016).

MedlinePlus. “Restless Legs.” U.S. National Library of Medicine, National Institutes of Health. (accessed July 10, 2016).

MedlinePlus. “Sleep Apnea.” U.S. National Library of Medicine, National Institutes of Health. (accessed July 10, 2016).


American Sleep Apnea Association. 1717 Pennsylvania Ave., NW, Suite 1025, Washington, DC 20006. Toll-free: 888-293-3650. Website: (accessed July 10, 2016). (accessed July 10, 2016).

National Heart, Lung, and Blood Institute. PO Box 30105, Bethesda, MD 20824-0105. Telephone: 301-592-8573. Website: (accessed July 10, 2016).

National Sleep Foundation. 1010 N. Glebe Rd., Suite 420, Arlington, VA 22201. Telephone: 703-243-1697. Website: (accessed July 10, 2016).

* electroencephalogram, or EEG, is an instrument that records the electrical activity of the brain.

* adenoids (AH-din-oyds) the fleshy lumps of tissue behind the nose that contain collections of infection-fighting cells of the immune system

* tonsils are paired clusters of lymphatic tissue in the throat that help protect the body from bacteria and viruses that enter through a person's nose or mouth.

* stroke is a brain-damaging event usually caused by interference with blood flow to the brain.

* hallucinations (ha-LOO-sin-AY-shuns) occur when a person sees or hears things that are not really there. Hallucinations can result from nervous system abnormalities, mental disorders, or the use of certain drugs.

* paralysis (pah-RAH-luh-sis) is the loss or impairment of the ability to move some part of the body.

* depression (de-PRESH-un) is a mental state characterized by feelings of sadness, despair, and discouragement.

* oxygen (OK-si-jen) is an odorless, colorless gas essential for the human body. It is taken in through the lungs and delivered to the body by the bloodstream.

* psychotherapy (SY-ko-THER-a-pea) is the treatment of mental and behavioral disorders by support and insight to encourage healthy behavior patterns and personality growth.

  This information is not a tool for self-diagnosis or a substitute for professional care.