My dad died in his late 80s of Parkinson's. For at least a decade before his diagnosis he'd tell me that everyday when he woke up, he'd lost another piece of himself. He went from an active man in his early to mid 70s--he rode his bike 25 miles a day and weight lifted--to a shadow of himself very quickly.
It was tough to watch, and so much tougher for him facing loss after loss of his abilities. He spoke several times of "releasing" himself, but ultimately decided not to do it.
We are living longer, but that isn't always to our benefit.