My mother has dementia and stays in bed day and night. Is it normal?

I'd discuss it with her doctor. It may depend on the stage that she's in. I know that in the early stage, my LO slept A LOT. She did not want to get out of bed, but, it must have been related to depression, because once she got on medication, she started being more alert and active during the day. Plus, she was around more people at the AL and they saw to it that she got up and had meals, got meds, bathed, etc.

However, as the dementia progresses, I've read that in the later stages, the patient becomes more and more bed bound. And their sleep increases. So, I'd check with her doctor to see what might be going on with her. You might have her thyroid checked too. That can make you very tired if there is an imbalance.

No, it's not normal unless she is at the end of life.

Is she on an antidepressant?