Delirium, also known as acute confusional state, is the organically caused decline from a previous baseline mental functioning that develops over a short period of time, typically hours to days. Delirium is a syndrome encompassing disturbances in attention, consciousness, and cognition. It may also involve other neurological deficits, such as psychomotor disturbances, impaired sleep-wake cycle, emotional disturbances, and perceptual disturbances, although these features are not required for diagnosis.