Age-related diseases such as Alzheimer's make life difficult for some elderly people and their family members. Do you have any experience with this in your family?
My paternal grandma had it but I was still quite young. I only remember snippets from my parents. She'd have some good days, would joke with you. Then there were days she was moody, crabby, & didn't know who you were.
It's heart-wrenching to have to go through for the person suffering & for the family.