Narcolepsy, the main characteristic of which is excessive and overwhelming daytime sleepiness, is a chronic sleep disorder with no known cause.

You should be checked for narcolepsy if you:

• often feel excessively and uncontrollably sleepy during the day even after a full night's sleep.
• fall asleep when you do not intend to, such as while having dinner, talking, or working.
• collapse suddenly or your neck muscles feel too weak to hold up your head when you laugh, become angry, or express other emotions. This symptom is called cataplexy.
• find yourself briefly unable to talk or move while falling asleep or waking up. This is referred to as sleep paralysis.
• have vivid, often frightening, dream-like experiences while dozing or falling asleep. This is called hypnagogic hallucinations.

Normally, when a person falls asleep, he falls into a state called non-rapid eye movement (NREM) sleep during which brain waves become slower and less regular. After some 90 minutes, the individual enters rapid eye movement (REM) sleep, a state in which brain waves are more active and in which dreaming occurs. In narcolepsy, the order and length of NREM and REM sleep periods is disturbed, with REM sleep occurring at the beginning of sleep.

Two tests are generally used to diagnose narcolepsy. The polysomnogram, or sleep recording, records brain waves and several nerve and muscle functions during sleep. The multiple sleep latency test calls for an individual to sleep every two hours during normal wake times. This allows a physician to observe the time it takes for a person to reach various stages of sleep.

Although there is yet no cure for narcolepsy, drug therapy and lifestyle changes can help patients manage their condition.