Narcolepsy
Human narcolepsy manifests itself in unstable wakefulness, sleep, and REM-sleep states. The orexin/hypocretin system (brain neuronal system), is associated with the stability of being awake and asleep. When narcolepsy is present, it causes a dysfunction of this system and the awake state becomes unstable. People with Narcolepsy have sleepiness and may fall asleep unexpectedly. They also wake up frequently and experience fragmented sleep. REM-sleep is unstable as well. REM-sleep has two components—one is associated with dreaming, and the other causes adult humans to be almost paralyzed during REM-sleep. (Except for eye muscles and respiratory muscles).
In Narcoleptics, the components of REM-sleep may not occur at a proper time. The paralysis of REM may occur immediately after waking up. This is called sleep paralysis. The paralysis may start to happen with emotions, such as laughter. This is called cataplexy. Furthermore, dreaming may happen immediately after awaking or while falling asleep. These are called hypnagogic or hypnapompic hallucinations.
Narcolepsy is not a life threatening or dangerous condition; however, one of the main risks involved, are car accidents. Narcoleptics should not be involved with certain professions, including flying or operating machinery. Fortunately, Narcolepsy can be managed with medication.