Delirium

Delirium is characterized by a sudden onset of disorganization of higher mental processes. It is caused by a generalized disturbance in brain metabolism such that a person may have significant difficulty with basic cognitive processes. Such processes include perception, attention, memory, and thinking. Many individuals also experience sleep disruptions and psychomotor difficulties. Delirium is, in a relative sense, one step away from coma. Individuals suffering from delirium no longer have the ability to carry out purposeful mental activity of any kind. They have abnormal responses (either lethargy or agitation) to environmental stimuli, and they often experience hallucinations, misperceptions, and paranoia. Episodes of delirium rarely last more than a few days and may result from fever, head injuries, drugs, or oxygen deprivation to the brain. The most common causes of delirium are physical disease, brain injury, and drug abuse.

Please note that the following information on dementia, up to but not including the stages of dementia, has been reprinted from the Mayo Foundation for Medical Education.