Delirium 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. People with delirium may experience other neuropsychiatric disturbances including changes in psychomotor activity, disrupted sleep–wake cycle, emotional disturbances, disturbances of consciousness, or altered state of consciousness, as well as perceptual disturbances, although these features are not required for diagnosis.