I sincerely hope you never experience dementia Rick. I went through it with my mother. As her only child, I was the major caretaker. Even after she went into a nursing home...I was there daily (unless I was sick) and sometimes twice during the day. She was usually her sweet self during the day but when "sundowning" happened, she was in a hellish world that I sometimes got dragged into. It was astonishing, frightening and heartbreaking. I think I posted more detail about it in another thread. If I find that post, I'll repost it here.
Now my half sister (we really don't like using that term) is going through it. I'm not her major caregiver so I get bits and pieces of what's happening to her but am not immersed in it. We used to take vacations together and I recognized when it first started happening a few years ago, but no one else close to her wanted to acknowledge it. Now her children, our nieces and her S.O., have no choice. It is so hard watching loved ones slipping into darkness!