My wife turns on the bedroom light around 3 am and asks if our friends or grandkids are still here. I always tell her "No, they have gone." She is in the Middle Stage of dementia. Sometimes, if she won't turn off the light, I have threatened to sleep in the guest bedroom, but she says she doesn't want me to do that. What should I do the next time?
Try to help her burn energy during the day: folding towels, walking around the house, reading aloud, sorting things, playing cars or board games etc. Once we had my Aunt with advanced dementia do this she began sleeping through the night without any sleep aids. Its not a perfect solution but may help her.
Sundown usually happens in late afternoon, early evening, when the sun is going down. If your not sure if a person is suffering from Dementia this is the time you know they are. It could happen because this is when the brain becomes tired because some are aware there is something wrong and can "showtime". I go down with the Sun so something in the brain? Some sundown earlier some later. Eventually, though, that will stop as the Dementia worsen.