III. Hypersomnia
Narcolepsy and recurrent hypersomnia are disorders of excessive sleepiness. Hypersomnolence can be caused by numerous disorders including narcolepsy, apnea, sleep-disordered breathing, or periodic limb movements in sleep. One of the most common causes of hypersomnia is behaviorally induced insufficient sleep syndrome.
Narcolepsy
Narcolepsy is characterized by severe sleepiness, episodes of sudden weakness called cataplexy, sleep-onset hallucinations, sleep paralysis on wakening, and fragmented nocturnal sleep. Cataplexy is the name for brief periods of paralysis or loss of muscle tone while a person is awake, often brought on by excitement, anger, or laughing. The onset of narcolepsy usually occurs in adolescence or early adulthood, and it persists throughout life. Most patients have some, but not all, of these symptoms. Narcolepsy with cataplexy can be diagnosed clinically. Narcolepsy without cataplexy is diagnosed by the typical finding of multiple REM sleep periods during a multiple sleep latency test (MSLT).
In recent years scientists have discovered a new brain chemical, hypocretin, which helps control REM sleep. People with narcolepsy lack this chemical or have very low levels. Symptoms of narcolepsy are usually controlled by medications, including amphetamines and other stimulants, to promote alertness. A newer medication, sodium oxybate, is given to narcoleptics during sleep and improves sleepiness and cataplexy.
Patients who have severe sleepiness without cataplexy, and who do not have multiple REM periods on the MSLT, may be diagnosed with idiopathic hypersomnolence. In one type of idiopathic hypersomnolence, patients sleep at least ten hours daily and still are sleepy.