rbart, my thoughts are with you.
Dementia is tough. My father's mother got sick very fast. I remember visiting her in the institution. I was about 14 then. She started swearing in Russian, then started saying in English "Who is that man? Get that man out of my room". It's hard to forget that.
My father passed while I was in college. He never met my wife, never met my kids. Cherish the time you have with your parents, because it is fleeting.