How do i know if my mother sleeps all night,she had dementia?

mom is 91 yrs.old has dementia how do i find out if she sleeps all night.my sister and i are caregivers?when she gets up in the am.she looks tired and sleeps most of the day.we are worried.her dr.says she is coming along fine,i wonder about that.she also has a terrible temper when she has been woken up by noise.has no kind of activity at all to say the least.she doesn't want to be bothered. can anyone help