NYU Professor of Neurology Oliver Sacks spills the beans on hallucinations in the New York Times:
Hallucinations are very startling and frightening: you suddenly see, or hear or smell something — something that is not there. Your immediate, bewildered feeling is, what is going on? Where is this coming from? The hallucination is convincingly real, produced by the same neural pathways as actual perception, and yet no one else seems to see it. And then you are forced to the conclusion that something — something unprecedented — is happening in your own brain or mind. Are you going insane, getting dementia, having a stroke?
In other cultures, hallucinations have been regarded as gifts from the gods or the Muses, but in modern times they seem to carry an ominous significance in the public (and also the medical) mind, as portents of severe mental or neurological disorders. Having hallucinations is a fearful secret for many people — millions of people — never to be mentioned, hardly to be acknowledged to oneself, and yet far from uncommon. The vast majority are benign — and, indeed, in many circumstances, perfectly normal. Most of us have experienced them from time to time, during a fever or with the sensory monotony of a desert or empty road, or sometimes, seemingly, out of the blue.
Many of us, as we lie in bed with closed eyes, awaiting sleep, have so-called hypnagogic hallucinations — geometric patterns, or faces, sometimes landscapes. Such patterns or scenes may be almost too faint to notice, or they may be very elaborate, brilliantly colored and rapidly changing — people used to compare them to slide shows.
At the other end of sleep are hypnopompic hallucinations, seen with open eyes, upon first waking. These may be ordinary (an intensification of color perhaps, or someone calling your name) or terrifying (especially if combined with sleep paralysis) — a vast spider, a pterodactyl above the bed, poised to strike.
Hallucinations (of sight, sound, smell or other sensations) can be associated with migraine or seizures, with fever or delirium. In chronic disease hospitals, nursing homes, and I.C.U.’s, hallucinations are often a result of too many medications and interactions between them, compounded by illness, anxiety and unfamiliar surroundings.
But hallucinations can have a positive and comforting role, too — this is especially true with bereavement hallucinations, seeing the face or hearing the voice of one’s deceased spouse, siblings, parents or child — and may play an important part in the mourning process. Such bereavement hallucinations frequently occur in the first year or two of bereavement, when they are most “needed.”…