hallucination

(hă-loos-ĭ-nā′shŏn )

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[L. hallucinari, to wander in one's mind]
A false perception having no relation to reality and not accounted for by any exterior stimulus. It is a dreamlike or nightmarish perception occurring while awake. It may be visual, esp. in medical illnesses or drug withdrawal syndromes; auditory, esp. in psychoses; tactile; gustatory; or olfactory. Affected patients typically appear confused and agitated and are unable to distinguish between the real and the imaginary.
SEE: delusion; SEE: illusion

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