Overview of Common Sleep Disorders

Sleep Apnea, Insomnia and More

Woman lying awake in bed
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Many medical conditions may lead to a disruption of sleep, or an excessive amount of daytime sleepiness, and are called sleep disorders. These may be caused by physiological or psychological factors. Some of the more common sleep disorders include:

Snoring and Sleep Apnea

Snoring may seem benign, but it may represent a difficulty in keeping the throat open while one sleeps.

Its more serious companion, sleep apnea, is a chronic medical condition where the affected person repeatedly stops breathing during sleep. These episodes last 10 seconds or more and cause oxygen levels in the blood to drop. It can be caused by obstruction of the upper airway, resulting in obstructive sleep apnea, or by a failure of the brain to initiate a breath, called central sleep apnea. It can cause and worsen other medical conditions, including hypertension, heart failure, and diabetes.


Insomnia is an inability to obtain a sufficient amount of sleep to feel rested and can be characterized either by difficulty falling or staying asleep. It is the most common sleep disorder, with many potential causes. One of the sub-types is acute insomnia and a rare type that runs in families may even be fatal.


From the Latin meaning "around sleep," parasomnias are a sleep disorder characterized by abnormal sleep behaviors.

Parasomnias involve unconscious complex, semi-purposeful, and goal-directed behaviors that have meaning or importance to the individual. These can include sleep terrors, sleepwalking, sleep eating, sleep sex, rapid eye movement (REM) behavior disorder, or any number of potential behaviors that occur while the person remains asleep.

Sleep Paralysis

Sleep paralysis is characterized by a temporary inability to move while transitioning from sleep to wakefulness, such as when falling asleep or waking up. It may be frightening as one may seem to be awake, but unable to move. It is common, but may also be a symptom of narcolepsy.

Restless Legs Syndrome

Restless legs syndrome is a neurological movement disorder characterized by unpleasant feelings in the legs associated with a need to move. These sensations may include aches, burning, tingling, or the feeling of bugs crawling on the legs. These symptoms may occur at rest or at night making it hard to fall or stay asleep. RLS has many potential causes, including iron deficiency, pregnancy, and obesity. It may be associated with periodic limb movements of sleep (PLMS)

Circadian Rhythm Disorders

Circadian rhythm disorders are conditions that may result when an individual’s internal biological clock is out of sync with external time cues, including the natural dark-light cycle. This may occur in total blindness, with shift work or jet lag, or due to advanced or delayed sleep phase syndrome. The mismatch may lead to insomnia or hypersomnia at inappropriate times.


Narcolepsy is a sleep disorder characterized by four classic symptoms: excessive daytime sleepiness, cataplexy, sleep paralysis, and hypnagogic hallucinations.

The sleepiness can be profound and may lead to falling asleep in inappropriate situations. Cataplexy is a loss of muscle tone in response to an emotional stimulus, such as surprise or laughter. Sleep paralysis is an inability to move one's body while being awake, usually while falling asleep or awakening. Hypnagogic hallucinations are vivid dream-like auditory, visual, or tactile sensations that occur while falling asleep.

Chronic Fatigue Syndrome

Chronic fatigue syndrome (CFS) is characterized by unexplained prolonged fatigue that is not improved by rest and may be worsened by physical or mental activity.

This fatigue can be severe and incapacitating, causing a substantial reduction in daily activities. It may require adaptations to conserve energy in extreme fatigue. There are a number of associated symptoms, and other medical conditions must be excluded before CFS can be diagnosed.

Jet Lag

Jet lag is a temporary condition caused by rapid travel across time zones -- as may occur with jet trips -- and may leave an individual experiencing fatigue, insomnia, nausea, or other symptoms as a result of the internal circadian rhythm, or body clock, being misaligned with local time.

Seasonal Affective Disorder

Seasonal affective disorder is a recurrent mood disorder associated with depression and excessive sleepiness during winter months. It is caused by a lack of bright light reaching the biological clock in the suprachiasmatic nucleus, a small region of the brain. Its treatment is the use of a light box to artificially extend the day length.


Kryger, MH et al. "Principles and Practice of Sleep Medicine." Elsevier, 5th edition.

"The International Classification of Sleep Disorders." American Academy of Sleep Medicine, 2nd edition, 2005.