: a perception of something (as a visual image or a sound) with no external cause usually arising from a disorder of the nervous system (as in delirium tremens or in functional psychosis without known neurological disease) or in response to drugs (as LSD)—compare delusion 2, illusion 2a
: the object of a hallucinatory perception
Perception of objects, sounds, or sensations having no demonstrable reality, usually arising from a disorder of the nervous system or in response to certain drugs (seehallucinogen). Hallucinations are in many ways similar to dreams: they derive their content from perceptions known to memory, though these can be greatly transformed. Hallucinations can result when attention collapses from intense arousal due to extreme anxiety, fatigue, excitement, or other causes. They figure prominently in the diagnosis of schizophrenia.