Delirium may be of a hyperactive variety manifested by 'positive' symptoms of agitation or combativeness, or it may be of a hypoactive variety (often referred to as 'quiet' Delirium) manifested by 'negative' symptoms such as inability to converse or focus attention or follow commands. While the common non-medical view of a delirious patient is one who is hallucinating, most people who are medically delirious do not have either hallucinations or delusions. Delirium is commonly associated with a disturbance of consciousness (eg, reduced clarity of awareness of the environment). The change in cognition (memory deficit, disorientation, language disturbance) or the development of a perceptual disturbance, must be one that is not better accounted for by a preexisting, established, or evolving dementia. Usually the rapidly fluctuating time course of Delirium is used to help in the latter distinction.   Wikipedia