My grandfather survived a few cancer appearances but during the last surgery to remove some cancer lumps he woke up as a completely new person. It seems the anesthesia triggered the first signs of Parkinson's and dementia exactly at the same time. He was pretty "normal" before the surgery but after it he couldn't walk and thought the hospital staff attacked him with dogs during the night. Fortunately (?) he didn't last long after that day but still had time to be kicked off from his home by my grandmother who couldn't handle the dementia.
Sorry for the rant, I'm obviously not over it, will never be. Dementia is the worst thing I've ever witnessed.