My mother is 77 years old and has suffered with vascular dementia since 2010. I'm not understanding why she sleeps much of the day. She is woken up by the caregivers to be feed. She eats and drinks well, though she doesn't feed herself, but continues to lose weight. She is very thin and frail with body stiffness. No longer able to hold her neck up or torso.
Also ask hospice whether it is a good thing to wake mom up to feed her.
The only thing I can offer is that if she is in "end stage hospice care", that indicates that he is perhaps nearing the end of her life - which would explain why she is sleeping a lot. That's completely normal for someone nearing the end.
I would strongly recommend asking these questions of her physician if you're concerned.