Mom in final stage of Alzheimer's sleeps 18+ hours/day. I have never seen this before. Why is she sleeping so much?

Thank you for this question and thank you for the answers. My mother is 88 and has been sleeping most of the day and of course I change her and feed her but at times she is so sound asleep she sleeps through a changing of clothing. Like others she takes naps and it scares the heck out of me.

Look forward to hearing more from others and thanks!

It seems they spend the time they are awake trying so hard to speak or do anything else that they totally wear themselves out and therefore sleep until they eat and that takes so much energy again they go back to sleep.

It seems to be what happens as they are winding down. I don't know of any "scientific" explanation, but I am sure there is one. My mother ate less and less and slept more and more in the 6 months before she passed. Their brains are broken and their bodies are worn out,

An ER doctor told me "sometimes they just get tired" - he was an ass but there was some truth to his words, as the years creep up and diseases progress they do become tired, both in body and mind. My mom used to go back to bed after breakfast and sleep until lunch, she had a little nap in the afternoon too before her 8:00 bedtime and this was at least 5 years before she was end stage - by then she existed mostly in the twilight zone and was really only awake at meals or when she was being care for.