As late as the 18th century, hallucinations in their various forms were considered independent diseases or syndromes. In 1821, Alexis Vincent Charles Berbiguier de Terre-Neuve du Thym, a French author and demonologist, published a three-volume book entitled The Imps; or, All the demons are not from the other world, in which he described frequent torments by small mischievous devils. In 1816, Berbiguier became a patient of the French physician Philippe Pinel, a pioneer of psychotherapy.
…The concept that hallucinations were not a disease per se but a “symptom” of different diseases developed in the 19th century after what one leading psychiatrist called a “long and barren” debate. Although hallucinations are now regarded as symptomatic of a number of disorders, they are not themselves necessarily harmful. As a symptom, they can indicate that the brain is not functioning properly, which may lead to other harmful symptoms, but hallucinations are not categorically good or bad.
Some people, both those with and without mental illness or a neurological disorder, actually enjoy their hallucinations. People who experience visual hallucinations following a bereavement, for example, can find them comforting.
Hallucinations force us to question the very nature of reality. Unlike imagination, hallucinations don’t seem to be of our own creation, are often outside of our control, seem to come from the outside world, and mimic perception.
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