Hypnagogic Hallucinations and Sleep Paralysis

Hypnagogic hallucinations and sleep paralysis are two associated features of narcolepsy that can also be found as isolated phenomena or within the context of other clinical conditions. Hypnagogic hallucinations are abnormal sensory perceptions experienced in the transition between wakefulness and sleep, whereas analogous hallucinations that occur upon awakening are called hypnopompic. Sleep paralysis is a transient paralysis of skeletal muscles associated with a clear waking mentation occurring in sleep/wake transitions. The two phenomena often occur together in narcoleptic subjects, provoking significant fear responses, especially when first experienced, because of the threatening and often terrifying content of the hallucinations and the impotence associated with the inability to move.