My father's side of the family is riddled with mental illness and addiction. Dad died in his mid-fifties after decades of hard drug use. The upside to this is that when I do the "death math" and try to estimate what age I might naturally die based on my family history, he definitely lowers the average a bit.
My maternal grandmother had a stroke and spent the last 15-ish years of her life in a nursing home completely nonverbal and unable to feed/wash/toilet herself. Seeing her like that and fearing a similar fate is part of why I'd like to die on my own terms. I just have this awful feeling I'm going to end up like her if I stick around long enough.
It's vain, but I honestly think more about the awful-shaped body I inherited from my mother. I saw the efforts she went to to hide herself with dark, loose, modest clothing and I just have to ask myself why she'd have a child knowing that there was a 50% chance of having a daughter and then another 50% of her ending up trapped in a horrible shell like this.