There are days when my mum sleeps virtually all the time. Her carers get her up in the morning, wash and dress her and transfer her from her bedroom to her lounge (which she still retains as 'her' space although we live in the same house. Some days she doesn't even stay awake long enough to eat her breakfast or take her medication, and we let her lie back on the sofa with her feet up, hot water bottles, and blankets until she wakes. I take the view that as she has dementia and is confused and upset for about 75% of her waking hours, whilst she's asleep we are doing her a service. But as pamstegma says, you need to be careful about pressure sores. If your mum's asleep in bed then you should get an air mattress for her because this will help, but she needs hot water bottles with such a mattress because these things are cold as the air that circulates within them is cold. Also, to ward off pressure sores you could use ProShield as a regular washing soap for her - this protects the integrity of skin that spends a lot of time compressed. What is interesting about the sleep pattern is that it's not really a pattern - some days my mum's wide awake, and if we take her out she can remain awake for a long time although the following day she may sleep for 18 hours. I think if you are keeping your mum comfortable you're doing as much as you can.
I'm not sure (not that anyone can be completely sure - we are frail humans trying to figure out and make time for what is best in the way of care for the vulnerable who sometimes don't speak in ways that seem to make sense). I've struggled with such questions when my pets were ill with death coming. Best thing I can think of, is make some time and a schedule, that you are able to do, to be with her, in the room, for maybe half hour or 45 min at a time. You might sit on the bed and read, or sew, have a nap. Allow her to sleep but be close by. I think it is sad to wait for the fragile to ask for what they need - part of what we/they need, is the comfort of predictability in some basic routine and schedule, and the experience that even if we cannot talk, we want to know we are loved and valued. I have found as caregiver, even for dying pets - the conflicts of interest of where to spend energy, are exhausting in themselves. You make time to pay attention, only to find it wasted, as the opposite symptom returns, or you feel hope, only to find that after 2-3 days, it's back to deterioration again. You worry about the many life needs that are going unaddressed during this period, or may even worry about how to have enough money to last through care.
On the other hand, there are moments which bring back such reward of love still shared. I like to think I am someone who made the time, and worked to sit close, maybe read aloud, or do something gentle, so that I played the role which I believe in doing, and after they passed, I slept better for making some deliberate time. It's not necessary to do too much, or respond to every whim - only necessary to be kind and make some time to be present and show care - maybe 2-3 half hour periods in a day, and follow SOME routine, so they can rely on that.
On the other hand, there are moments which bring back such reward of love still shared. I like to think I am someone who made the time, and worked to sit close, maybe read aloud, or do something gentle, so that I played the role which I believe in doing, and after they passed, I slept better for making some deliberate time. It's not necessary to do too much, or respond to every whim - only necessary to be kind and make some time to be present and show care - maybe 2-3 half hour periods in a day, and follow SOME routine, so they can rely on that.