Disorder characterized by confusion, inattentiveness, disorientation, illusions, hallucinations, agitation and in some instances autonomic nervous system overactivity; may result from toxic or metabolic conditions or structural brain lesions; condition may also be acute and reversible.

Delirium (formerly acute confusional state, an ambiguous term that is now discouraged) is a specific state of acute confusion attributable to the direct physiological consequence of a medical condition, effects of a psychoactive substance, or multiple causes, which usually develops over the course of hours to days. As a syndrome, delirium presents with disturbances in attention, awareness, and higher-order cognition...