Yes, delirium is the medical name for it. Delusions can be a symptom of delerium. I can speak to it pretty well because as a hospital nurse I deal with it all the time, and also had to deal with it in my own mother when she was a patient. It is a result of a lot of chemicals in the body becoming out of whack, usually as a result of an illness, surgery, medications, low oxygen levels, hospitalization itself (with days and nights mixed up), infection, electrolyte disturbances, etc. It usually comes on quicker and can resolve. It can get worse at night. (Sundowning.)