Many doctors can attest that there is nothing like poor sleep to affect you outlook on life. (There is an old joke that even though doctors might die sooner than other people, they've spent more time awake.) Disturbed sleep, especially occurring in a person with severe dementia, can be the final straw in a caregivers' ability to cope, and therefore is a common cause of seeking to have a person with dementia admitted to institutional care.

Fortunately, sleep disturbances often respond well to treatment with a variety of medications. Unfortunately, many have side effects, and particularly can make the person's thinking and cognition Cognition
The mental processes associated with knowing and understanding thoughts and perceptions about one's environment. worse during the day.

When sleep disturbances come on acutely, they can be a marker of delirium, which is usually caused by medications, or by an acute illness, such as an infection, or heart disease, or out-of-control blood sugars. As such, it merits prompt attention by a doctor.