Narcolepsy is a sleep disorder characterized by sleepiness (sleep attacks, need to nap during the day), cataplexy (being weak or paralyzed when laughing, angry or during sudden emotions) and disturbed sleep (insomnia, vivid dreaming, being paralyzed but awake when waking up). Not all patients have all symptoms. When cataplexy is present, the disorder is almost always due to a destruction by the immune system of about 70,000 brain cells that produce a chemical called hypocretin. As this chemical helps in staying awake and regulating sleep and muscle tone, the lack of hypocretin explains all the symptoms of narcolepsy. In these cases of narcolepsy, the disease is life-long and does not resolve. When cataplexy is not present, many causes may be involved and the diagnosis is more difficult. Evolution and response to treatment are also more variable. Narcolepsy is diagnosed using sleep tests, biochemical measures and occasionally by measuring hypocretin in the cerebrospinal fluid (CSF) after a lumbar puncture. Current treatments involve medication and behavioral, life styles changes.