A hallucination is a perception in the absence of a stimulus that the person may or may not believe is real. Hallucinations may occur in any sensory modality?visual, auditory, olfactory, gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, thermoceptive. Hallucinations are different from illusions. In an illusory experience, a genuine sensation is attributed to an incorrect cause, misinterpreting a coat hanging on a door to be an intruder or thinking there is water on a hot road, due to the heat rising from the road. A delusional perception is where a genuine perception (ie. correctly sensed and interpreted) is given some additional (and typically bizarre) significance. Hypnagogic hallucinations and hypnopompic hallucination are considered normal phenomena. Hypnagogic hallucinations can occur as one is falling asleep and hypnopompic hallucinations occur when one is waking up. Hallucinations may also be associated with drug use (particularly hallucinog