For reals, it wasn't fun to watch my great-grandmother slowly lose herself to dementia, she had it for over a decade before she finally died. She apparently started getting it while I was still in elementary school, because there was a time when we were staying at my grandparents' place before our move, and our great-grandparents lived just down the street, so my brothers and I would sometimes visit after school. Then at some point my mom and grandmother just took us aside and asked us to not visit them alone anymore. Turned out that in the early stages of dementia, Great-Grandma thought they were being burglarized and we could've been falsely blamed for it. They were put into a group home about a few years after that, and when I was about sixteen Great-Grandpa died while the twins and I were out for a church youth group thing for that week, so we didn't get to go to the funeral. Great-Grandma had been forgetting about him by then and from what I was told, she just thought he was asleep the whole time and was grouchy at him because of it (she held a bit of a grudge toward him thanks to dementia, and that's why we think it took her so long to pass on).
I would visit Great-Grandma a few times during college, but it was just super uncomfortable being at a group home because it just never felt right (and I don't think it had anything to do with the elderly), and it also just sucked to see her like that. The last time I saw her, she just casually let me pick out a stuffed animal from her collection that I still sleep with, and while Grandma and her were in the front room, I ended up wandering off to one of the back rooms because an elderly woman kept calling out for help as she got stuck trying to get out of bed. After one of the nurses came in to fix her up (I tried to help, but I'm not strong enough for it and it just wasn't my job anyway, got scolded for it), I stayed to keep her company for a little bit before Grandma came in looking for me. I was apparently her only visitor in a long time (her children never visited), and when we left around their lunchtime, I gave the old lady a little hug. She passed away shortly after that, and I just didn't want to go back there anymore, it was too upsetting for me. So I didn't see Great-Grandma again until her funeral a few years ago.
Pretty sure that was much more traumatizing than when I was a twelve-year-old waking up to find my hamster dead (still not sure if it was old age or a disease I didn't catch in time).