The hallucinations, like sleep paralysis and cataplexy, are thought to be waking manifestations of REM sleep. These hallucinations normally involve a life like environment, such as objects in the bedroom moving. The hallucinations are classified as either hypnagogic or hypnopompic . Hypnagogic hallucinations occur just before falling asleep. Hypnopompic hallucinations occur just after waking up.
Hypnagogic hallucinations are the type usually associated with narcolepsy.
Approximately 30 to 50 percent of narcoleptics have periodic sleep paralysis, while about half of normal sleepers experience rare episodes of sleep paralysis. When this happens, the person feels as if he or she cannot move or breathe. These brief episodes, which can last from a few seconds to a few minutes, occur when a person is waking up or trying to fall asleep. Sleep paralysis, as well as hallucinations and cataplexy, are characteristics of REM sleep that can occur in a person's waking life. For instance, a person may drive to a friend's house and not remember anything about the ride over.