Disorientation, fluctuation, waxing and waning of the above symptoms, and acute or abrupt onset of such disturbances are other critical features of delirium.
Delirium is reversible, even in advanced illness.
Still, it may not be reversible in the last 24 to 48 hours of life, most likely because of irreversible processes such as multiple organ failure. At times, it is difficult to differentiate delirium from dementia because they frequently share clinical features such as disorientation and impaired memory, thinking, and judgment. One difference is that the temporal onset of symptoms is more subacute or chronically progressive in dementia than in delirium. Occasionally, delirium is superimposed on an underlying dementia, such as in the case of an elderly patient, an AIDS patient, or a patient with a paraneoplastic syndrome. Medical and nursing staff sometimes conclude that a new symptom is psychologically based without first ruling out all possible organic causes.