Disordered regulation of sleep-wake cycles characterized by excessive daytime sleepiness (despite feeling rested upon waking) and "sleep attacks" (rapid-onset, overwhelming sleepiness).

Caused by ↓ hypocretin (orexin) production in lateral hypothalamus. Strong genetic component.

Also associated with:- Hypnagogic (just before going to sleep) or hypnopompic (just before awakening) hallucinations.- Nocturnal and narcoleptic sleep episodes that start with REM sleep (sleep paralysis).- Cataplexy (loss of all muscle tone following strong emotional stimulus, such as laughter) in some patients.

Treatment: good sleep hygiene (scheduled naps, regular sleep schedule), daytime stimulants (eg, amphetamines, modafinil) and nighttime sodium oxybate (sodium salt of gamma-hydroxybutyric acid, GHB).