Narcolepsy is a chronic neurological disorder caused by the brain's inability to regulate sleep-wake cycles normally. People with narcolepsy often experience disturbed nocturnal sleep and an abnormal daytime sleep pattern, which often is confused with insomnia. Narcoleptics, when falling asleep, generally experience the REM stage of sleep within 5 minutes, while most people do not experience REM sleep until an hour or so later.
One of the many problems that some narcoleptics experience is cataplexy, a sudden muscular weakness brought on by strong emotions (though many people experience cataplexy without having an emotional trigger).
Narcolepsy is a neurological sleep disorder. It is not caused by mental illness or psychological problems. It is most likely affected by a number of genetic mutations and abnormalities that affect specific biologic factors in the brain, combined with an environmental trigger during the brain's development, such as a virus.