I am tired of the term 'sundowners' and suggestions of lighting and scheduling. Habits are developed by learning, or appeal. They must find something appealing about staying up all night, in the early stages of dementia. What are the fears then of the daytime hours? My mother knows who the family is and the difference between night and day, although "I had no idea it was so late!" is a common statement. Yet she continues to sleep from dawn until dusk, after piddling around the kitchen. We have gone on trips, and managed to "reschedule" her routine fairly easily, for that period. She will go to bed at a reasonable hour and wake up with the rest of us. Upon coming home, however it isn't long before she reverts back to staying up all night. There has to be something other than a screwed up internal clock, or confusing night and day. Certainly someone can postulate as to "why" and not just tell this is part and parcel of dementia/Alzheimers, and leave it at that.