Dementia sleeping 20 hours per day?

My first question would be: have you been seeing a progression of more and more sleep, or is this a sudden change? When my mother-in-law took a bad fall, seemed to rally pretty good but then started sleeping more and more, we knew she was winding down. She was in a memory care unit, and after the face plant she took, we decided to bring hospice in when the ER Dr. said he didn't believe she had much longer. Before her fall, she was up walking and 'talking' and could still communicate, (well Alzheimers communicate), with us. One of the first signs tho was sleeping A LOT, then came not wanting to eat hardly anymore. She was 93. So if this is a new thing or a progressive thing, probably a doctor ought to take a look at her anyway.

I think sometimes the shorter winter days lead to longer sleeping periods. If she is also losing weight, then ask the MD for a prognosis. He may run some blood tests.