My partner had Vascular Dementia and spent the last few years mostly on his bed. He said he was listening to the radio, not sleeping, but I think it was a mixture of both. Initially I was worried by this, and tried to get him up and following the routine he had before, but then decided that it was the way PWD cope with the way their world has become - confusing, challenging, frightening - and that bed was the place they felt safe(r) and they did not have to deal with all the things that confused them - simple things like using the remote control for the TV, or answering questions, like "What would you like for supper?". He would come down, watch a bit of TV, eat whatever I put in front of him (usually), and was always up for a biscuit or some chocolate if all else failed, then back to bed, throughout the day. I would undress him and put him to bed after evening meal - around 6.30-7.00 p.m., and fortunately he would sleep (or at least not get up other than for toilet visits) until 5.00 am., when we would both get up, get dressed, breakfast, back upstairs - repeat, repeat throughout the day.
My advice would be not to worry about it, let them be where they want if they are safe, warm and comfortable, try to keep them clean (I know THAT is a challenge for many - it was for me!), and fed as best you can. Things will change, routines will change and we just have to adapt. After all, many times I have just wanted to crawl into bed, pull the covers up and stay there, shutting out the world and all the troubles, but, as carers of course, we can't do that.