Hallucinations

Patients may have vivid and often unpleasant auditory or visual hypnagogic hallucinations at sleep onset, either during daytime naps or at night.30 Hallucinations may occur on awakening; these hypnopompic hallucinations may be more characteristic of narcolepsy than the hypnagogic ones at sleep onset. The visual hallucinations usually consist of simple forms (colored circles, parts of objects) that are either constant or changing in size. The image of an animal or a person may present abruptly and more often in color. Auditory hallucinations are also common, although other senses are seldom involved. The auditory hallucinations can range from a collection of sounds to an elaborate melody. Hypnopompic hallucinations are often perceived as so vividly realistic that the patient acts on them on awakening. For example, patients with narcolepsy have been known to call the police because of intruders being in the home, only to discover after authorities have searched the house that it was all a hallucination. The exact boundary between hypnagogic/hypnopompic hallucinations and dreams is not a clear one. In some cases of unrecognized narcolepsy with daytime hypnagogic/hypnopompic hallucinations, the patient may be mistakenly diagnosed as having a psychosis.31

Another common and interesting type of hallucination reported at sleep onset involves elementary feelings (i.e., experiencing picking, rubbing, or light touching), changes in location of body parts (e.g., arm or leg), or feelings of levitation or extracorporeal experiences (e.g., the body in space or floating above the bed) that may be elaborate. For example, the patient may report, “I am above my bed and I can also see my body below” or “I am a few feet up and people are jumping over my body.” The abrupt motor inhibition that involves the spinal cord motor neurons may alter the feedback of information that is normally used by the central nervous system to gauge the position of the body and limbs.