Definition of Narcolepsy:

Narcolepsy is a sleep disorder that causes uncontrollable sleepiness and frequent daytime sleeping.

Causes, incidence, and risk factors:

The exact cause of narcolepsy is unknown. Studies using gene markers show that the disorder may be genetic. A small group of neurons in the brain has been implicated in producing transitions from sleep to wakefulness and vice-versa. People with narcolepsy may have fewer of these neurons, or these neurons may have been damaged.

The disorder may be aggravated by conditions that cause insomnia, such as disruption of work schedules.

Narcolepsy is characterized by episodes of frequent, uncontrollable daytime sleeping, usually preceded by drowsiness. Sometimes, the person may start dreaming immediately upon falling asleep. The episodes usually occur after meals, but falling asleep may occur while working or driving a vehicle, having a conversation, being in any non-stimulating situation, or being in situations where there is little movement (sedentary situations).

There is a brief period of sleep, and the person awakens feeling refreshed. However, the person may again become uncontrollably sleepy a short time later.

Narcolepsy may also be associated with cataplexy, a brief episode of severe loss of muscle tone in various muscles. Generalized weakness may occur for a few moments during the transition between sleep and wakefulness (sleep paralysis). Many people with narcolepsy also have dreamlike hallucinations in the transition between sleep and wakefulness.