What is the definition or description of: delirium?

Delirium: Delirium is a reversible condition whereby a patient is confused. It can be due to medication problems, metabolic disturbances, oxygenation, etc. It should be contrasted with dementia.

Classical def.: A rather acute state of confusion and disorientation, associated with agitation, hyper vigilance, irritability, and hallucinations, alternating with periods of depressed arousal. Many clinical problems can cause this, with the classic state: delirium tremens, associated with alcohol withdrawal.

Acute Brain Failure: We believe delirium occurs when the brain cannot maintain its normal activities when overwhelmed by metabolic demands or other variables which exceed the brain's capacity to compensate for. Brains with less reserve capacity are particularly vulnerable. Not entirely unlike acute heart failure. See my last textbook chapter for more reading in the appi textbook of psychiatry (5th ed).