Sleep napping all day. Any ideas why?

This is happening to my mom

She sleeps a lot and barely eats

As an elder progresses with Alzheimer's/dementia, they sleep a lot more and eat a lot less. It's a sign that the disease is advancing.

If you are unfamiliar with dementia, read and learn all you can about it so you can be armed with information to better understand what's going on.  
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Understanding the Dementia Experience, by Jennifer Ghent-Fuller 
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Best of luck to you.

My mother sleeps most of the day away. She gets up for meals, and when her hospice aide comes to give her a shower.

The exception is when the residents at her MC are baking cookies. She smells them, and out of her room she comes, happy to join in the eating. 🍪 🍪

It is happening more to my husband as well. Sleeps 12 hours, then naps as well, initially I thought it was from meds, it is more than that.

My Husband went from sleeping 8 hours to 10 then eventually to 12 then the last year it was about 20 hours the 6 months or so it was 23 hours. The only time he was awake was when he was eating, being showered or bathed and even changes of his briefs he often slept through.
Sleeping more, weight loss are 2 very common signs of decline that Hospice uses to recertify someone.

Yes, they sleep a lot more under even normal circumstances, and even more with dementia. It is very common. Less eating and more sleeping is the norm.