I fear dementia more than I fear death.
This. My father, who just passed this past year suffered from dementia, and while he had other health issues, including the cancer that finally claimed him, it complicated things to an incredible degree. Although, from the standpoint of a family member, I suppose it sort of helped with the grieving process, because in many ways, we lost him a long time ago, and the man who died that day in December, no longer really was my father, at least not the father I remember. The last few years were incredibly difficult, but his actual passing was surprisingly peaceful for me. Not that I didn't feel it, just that it was easier to say goodbye.
Now, for my own self, yeah, dementia seems like one of the most terrifying things I can think of. I love my brain, consciousness and memories. We're best friends. I can't think of much scarier than losing that.