My mum sleeps 17/18 hours too, some days. She goes to bed about midnight, then stays in bed until 4 or 5 in the afternoon. Some days, it's been near 6 oclock. When she finally gets up & I tell her how long she was in the bed, she looks at me as though I'm making it up & says no way. I worry as those days, she doesn't eat or drink from the eve before.

I ring her several times a day & tell her it's time to get up & eat. Says, just getting up, then when I go in to her she's still in bed. She just won't listen to me or my husband & always does the complete opposite of what we suggest or ask her to do.
Thankfully, I've managed to arrange for home help to go in 5 mornings a week & she gets my mum up after 9am, to have breakfast & tablets. Then I go in at 10.30 & take her to day centre. Now she's only in bed all day, on saturdays & sundays.

Home help has even managed to get her in the bath once a week. My mum said, she didn't feel like it & hasn't bathed since in hospital in Dec, when a nurse did it, she just washes with a flannel. Home help told my mum that she has other people to go into after her & if doesn't get her to bath, she'd lose her job. Thankfully, it worked both weeks. Funny how she eventually listens to outsiders & won't listen to family members, who do most things for her.

My husband sleeps up to 18 hours in 24.
I was told it is because only about half his brain works properly and even just living tires him out.
I also think it is his way of escaping from a life he finds hard to cope with.