A perceptual experience with all the compelling
subjective properties of a real sensory impression but without the normal
physical stimulus for that sensory modality. Hallucinations are taken as classic
indicators of a psychotic disturbance and are a hallmark of various disorders
like schizophrenia. Hence, the term is not usually applied to a variety of other
"false perceptions" that occur normally, like the images that often accompany
the transition from waking to sleeping (hypnagogic) or those that occur when
first awakening (hypnopompic) or those that occasionally accompany vivid
religious experiences. In actual usage the term is generally modified so that
the particular modality involved is specified, e.g., auditory hallucination,
tactile hallucination. Distinguish from Delusion.