"Some forms of dementia are reversible," Eleanor Goldberg, executive director of the Alzheimer's Association in Portland, says. "And, Alzheimer patients will have good days and bad days. Even a particular time of the day can be more difficult. The late afternoon is a tough time. It's called 'sundowning.' People become more anxious and their behavior escalates. It may be fatigue. They are trying to function when all of their brain capacity is not functioning at a normal level. It's exhausting," Goldberg says.

Even in the I.C.U., the psychosis often resolves spontaneously, with the coming of morning or sleep. Sometimes it lingers through the day. Severe agitation usually occurs only at night, however, which is why doctors and nurses often call it sundowning, also a kind of delirium common in nursing homes.

Conditions that can be confused with epilepsy include: … Acute confusion or "sundowning".