Delirium describes a sudden onset change in mental status of fluctuating course. This is a state of altered consciousness characterised chiefly by inattention or lack of arousal, but can also include new impairment of language, perception and behaviour. Certain predisposing factors can make an individual more susceptible to delirium in the face of a stressor. Stressors include direct insults to the brain, insults peripheral to the brain or external changes in the environment of an individual. Delirium is varied in its presentation, and can be categorised by the psychomotor profile as: hyperactive type (overly vigilant, agitated, often wandersome), hypoactive type (sedate or withdrawn) or mixed types.