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Hypersomniacs may feel compelled to nap repeatedly during the day, even if this still brings no relief
Hypersomniacs may feel compelled to nap repeatedly during the day, even if this still brings no relief
Hypersomnia, also called hypersomnolence or sometimes idiopathic hypersomnia (meaning that it arises from no known cause), is a sleep disorder characterized by excessive daytime sleepiness, excessive sleep periods each day (usually taken to mean more than 10 hours) and/or an inability to achieve the feeling of refreshment that sleep usually brings. Chronic sufferers may sleep up to 18 hours a day or more and still not feel refreshed upon waking. The disorder usually develops slowly over a period of years, typically starting in late adolescence, when it is often confused with normal teenage sleep issues like delayed sleep phase syndrome.

Hypersomniacs may feel compelled to nap repeatedly during the day, even if this still brings no relief. This may be due to some extent to a reported concomitant symptom of hypersomnia, the failure of the heart rate to decrease during sleep as it normally would, so that hypersomniac sleep may not be as restful per unit of time as normal sleep. Other symptoms may include anxiety, irritability, decreased energy, restlessness, slow thinking, slow speech, loss of appetite, hallucinations, memory difficulties and often severe sleep inertia on waking. These symptoms may be severe enough to affect a personís ability to function well in family, social and occupational settings. Normal hypersomnia, on the other hand, is a term sometimes applied to naturally "long sleepers".

In primary hypersomnia, the symptoms of hypersomnia may continue unabated for months or even years. In recurrent hypersomnia, the symptoms recur several times during the year, in between periods of relatively normal sleep-wake cycles, and may also be accompanied by other psychological disorders such as hypersexuality or compulsive eating. Kleine-Levin syndrome (also known as Sleeping Beauty syndrome) is an even more extreme variant of recurrent hypersomnia, first described by Willi Kleine in 1925 and then by Max Levin in 1929. It occurs almost exclusively in teenage boys, and sufferers may sleep for several days at a time, before waking ravenously hungry, irritable and oftern hypersexual.

Hypersomnia may be caused by other disorders such as depression, Celiac disease, mononucleosis or fibromyalgia, or it may arise as a by-product of other sleep disorders. It may also be in some cases an adverse reaction to certain medications, or result from drug or alcohol abuse. A genetic predisposition may also be a factor, as may excess weight. It is thought that the immediate mechanism for hypersomnia may be a particular somnogen (sleep-inducing substance) in the spinal fluid, although the substanceís exact identity and cause have still not been narrowed down.

Usually, prescribed stimulants are used to treat the symptoms, although these may be less effective for hypersomnia than they are for narcolepsy. Improved sleep hygiene and the avoidance of caffeine and alcohol are also usually recommended.