My Mother Is 80 And Was Diagnosed With Vascular Dementia

my mother is 80 and was diagnosed with vascular dementia 2-3 yrs ago and is getting worse and worse. she does not take any medication for it and just lately all she wants to do is sleep. we sing with her, watch TV and talk about what we are watching and I read to her. what is this excessive tiredness mean and what can we do about it please?