| Image = | Caption = | DiseasesDB = 29284 | ICD10 = | ICD9 = | ICDO = | OMIM = | MedlinePlus = | eMedicineSubj = med | eMedicineTopic = 3006 | MeshID = D003693 | }} Delirium is an acute and relatively sudden (developing over hours to days) decline in attention-focus, perception, and cognition. In medical usage it is not synonymous with drowsiness, and may occur without it. It 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. Because it represents a change in cognit