ABSTRACT
Sleepiness, cataplexy, hypnagogic hallucinations, and sleep paralysis have long been considered the tetrad of symptoms of narcolepsy. However, hypnagogic hallucinations and sleep paralysis are neither specific nor particularly sensitive for the diagnosis, and thus they should be considered ancillary clinical features with low diagnostic usefulness. Hypnagogic hallucinations, experienced in the transition between wakefulness and sleep, are usually visual but may be auditory, tactile, or vestibular. Similar experiences at sleep termination are known as hypnopompic hallucinations. Sleep paralysis refers to the transient inability to move, with preserved consciousness, at sleep onset or on wakening. Attacks of sleep paralysis may be accompanied by hallucinations and can often be aborted by touching the patient. About 25% of the normal population report having had hallucinations at sleep onset, and 7% describe episodes of sleep paralysis (7,8). In contrast, about 60% of patients with narcolepsy and cataplexy experience hypnagogic hallucinations and 66% experience sleep paralysis. However, only 32% of patients who have narcolepsy without cataplexy report having hypnagogic hallucinations and only 7% report sleep paralysis (9).
