Delirium is one of several causes of confusion. It is particularly common in elderly patients. Delirium causes consciousness to become clouded. Impaired awareness of the surrounding environment occurs. This may be as minor as simple misinterpretations and inattention or as severe as frank hallucinations. Patients often seem confused or disoriented as to time or place and may have visual or auditory hallucinations. Memory may be impaired. Sleep is often disturbed. Delirium develops quickly, typically within hours to days.