Narcolepsy is a chronic neurologic sleep disorder causing disruption in the normal sleep-wake cycle. It is characterized by overwhelming episodic daytime somnolence, momentary sleep paralysis, and rapid eye movement (REM) sleep with vivid visualization within minutes of falling asleep, rather than in the usual later stages of sleep. This excessive daytime sleepiness may be classified as narcolepsy type 1 (with cataplexy) or narcolepsy type 2 (without cataplexy). Cataplexy is a decrease in muscle tone triggered by emotions, with consciousness maintained. It typically lasts seconds to 1-2 minutes. It can interfere with daily functioning.

Narcolepsy type 1 affects about 1 in 2000 people. It tends to affect males and females equally. Age of onset is bimodal, at about age 15 and 35. Onset may be observed in school-aged children, but it is most often diagnosed in adolescence or the early 20s.

Other signs and symptoms include irritability, extended night sleep, difficulty waking, inattention, disrupted cognitive function, and mood and behavior dysfunction. Narcolepsy can lead to depression, obesity, and precocious puberty.

The etiology of narcolepsy is not fully understood. However, it is suspected that it is due to an autoimmune process that causes destruction of hypocretin (orexin) neurons in the hypothalamus. There is a strong association between narcolepsy and infection with Streptococcus pyogenes, and there was an increased incidence with the 2009 H1N1 influenza virus and the vaccine. Nearly all patients with type 1 narcolepsy are HLA DQB1*0602 positive compared to 12%-38% in the general population. In some situations, narcolepsy can be due to a medical condition. These include brain tumors, injury to the hypothalamus from cerebral lesions (vascular, sarcoidosis, demyelination) or a paraneoplastic disorder, congenital disorders such as Niemann-Pick disease type C, Parkinson disease, and residual excessive daytime sleepiness in those with adequately treated sleep apnea.

Management of symptoms involves lifestyle changes, good sleep habits, planned naps, and supportive counseling. Pharmacotherapy targets symptomatic relief and requires careful monitoring of undesirable side effects.