Why is my mom so sleepy all the time?

She is 88, almost 89, with moderate stage alzheimers. Since Dec. she has more days than not in which she is sleepy, regardless of how much she sleeps at night. She can hardly keep her eyes open, so is napping or just lying down most of the day. She perks up in the evening. All of her symptoms have worsened since just after Christmas and lately are getting a little more worse. We've had everything checked out and she's really healthy. She only takes a couple blood pressure medicines and started taking ativan .5mg for anxiety about 2 months ago. She usually only sleeps 5-6 hours straight a night but goes back to sleep after getting up to go to the bathroom. Is this sleepiness common with Alzheimers?