Alzheimer's. My mom dies of that and two other things. I cared for her alone 24/7 for a decade. Toward the end I could go out for a few minutes to do laundry or such. I could come back home while clothing spun to make a lunch for her then leave again. Upon returning I may be greeted by this sort of statement, "Oh, while you were here a nice lady came in and made me lunch." yeah, had been me.
The end of life is not much fun.
