Source : FISH ’S Clinical psychopathology

Hypnagogic and hypnopompic hallucinations

First mentioned by Aristotle, these hallucinations occur when the subject is falling asleep or waking up respectively. It has been suggested that hypnopompic hallucinations are often hypnagogic experiences that occur in the morning when the subject is waking and dosing-off again, so that they actually happen when the subject is falling asleep. The term ‘hypnopompic’

should be reserved for those hallucinatory experiences that persist from sleep when the eyes are open. Hypnagogic hallucinations occur during drowsiness, are discontinuous, appear to force themselves on the subject and do not form part of an experience in which the subject participates as they do in a dream. They are about three times more common (described by 37% of the adult population) than hypnopompic hallucinations, although the latter are a better indicator of narcolepsy. The subject believes that the hallucination has woken them up (for example, hearing the telephone ring even though it has not) and although the auditory modality is the most common it can also be visual, kinaestethic or tactile and is sudden in occurrence. Subjects describing hypnagogic hallucinations often assert that they are fully awake. This is not so and electroencephalogram (EEG) records show that there is a low of alpha rhythm at the time of the hallucination.

Hypnagogic visual hallucinations may be geometrical designs, abstract shapes, faces, figures or scenes from nature. Auditory hallucinations may be animal noises, music or voices. One of the most common is that of hearing one’s name called or a voice saying a sentence or phrase that has no discoverable meaning. In a subject deprived of sleep a hypnagogic state may occur, in which case there are hallucinatory voices, visual hallucinations, ideas of reference and no insight into the morbid phenomena. It resolves once the subject has a good sleep.

The importance of hypnagogic and hypnopompic phenomena is to recognise that they are not indicative of any psychopathology even though they are true hallucinatory experiences (Ohayon et al, 1996). They also occur in narcolepsy.