Definition of Excessive daytime sleepiness

Reviewed on 6/3/2021

Excessive daytime sleepiness: A neurological disorder in which there is a sudden recurrent uncontrollable compulsion to sleep. Excessive daytime sleepiness is also known as narcolepsy.

The condition is often associated with:

  • Cataplexy -- a sudden loss of muscle tone and paralysis of voluntary muscles associated with a strong emotion
  • Sleep paralysis -- immobility of the body that occurs in the transition from sleep to wakefulness
  • Hypnagogic hallucinations -- pre-sleep dreams
  • Automatic behaviors -- such as, for example, doing something "automatically" and not remembering afterwards how you did it.

More than 100,000 Americans have excessive daytime sleepiness (narcolepsy). It strikes both males and females and affects people of all races.

The symptoms most commonly appear in a person's teens and early twenties. The disease can vary in severity. Some persons with it have mild sleepiness or rare cataplexy (less than one episode per week). Other persons may have moderate sleepiness or infrequent cataplexy (less than one episode a day). Still other persons with the disorder may experience severe sleepiness or have severe cataplexy (with one or more episodes of cataplexy per day).

The basic cause of narcolepsy is not known. It is not a fatal disorder in itself but it can lead to fatalities. For example, a narcoleptic may fall asleep while driving.

Narcolepsy is usually treated with a medication to improve alertness and an anti-depressant that helps control cataplexy.

Other names for the condition include hypnolepsy, sleeping disease, paroxysmal sleep, and Gelineau syndrome.


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