My Mum is the same. Certainly over the last few months her energy levels have decreased. Even just going for short walk brings on a sleep when we get back. However I don't sleep at my mum's so I'm not sure how much sleeps she is getting on a night. I've also been informed by her GP that she is anemic too so this may be contributing to her been so lethargic.
Since my mother (aged 90) developed vascular dementia nearly 8 years ago she has needed a lot of sleep. She has her breakfast in bed at 8am then sleeps again until about 11am. Her carers get her up and she goes to the living room where she often naps until lunchtime. By 2pm she is exhausted. She goes back to bed from 2pm until 5pm. Then she gets up and goes back to the living room, having her supper at 7pm. She goes to bed at 8pm and sleeps for nearly 12 hours at night.
I think that, like a baby, she often wakes and lies thinking, but has not got the physical stamina to be 'up', even sitting in her wheelchair, for longer than she currently manages. Her GP says that she has no physical reserves of energy. On days when she has a morning shower she is really tired.
It is quite a relief to read these comments as I have been worrying about my Mum sleeping so much. She usually goes to bed about 9 and when I hear her go to the bathroom next morning I usually ask if she is ready to get up but she will scurry back to bed. I try to get her to drink a cup of tea during the morning but it is usually lunchtime or later before I can persuade her to get up and then she only wants to sit and doze in her chair. Twice a week she goes to day care and those mornings she will get up after I tell her she is going to her club but she usually needs a nap when she comes home.
Thank you everyone for showing me it is not unusual.