Before my grandmother died at the age of 95, she suffered from osteoporosis and emphysema, and had been for about 15 years or so. She wanted to die (she lost her husband 30 years prior, all of her siblings and friends). I didn't understand. When I was pregnant with my twins (4th pregnancy), by the end, I couldn't breathe (regulation size babies), and I was in SO much pain - back, hips, pelvis. I cried every night. My grandmother was still alive, and I couldn't imagine not only feeling the way I did, but knowing it was just going to get worse, and not better. I would've wanted to die, too. My greatest memory of their delivery was afterwards - I was giddy with my new ability to take a breath.
We allow our pets to be put to sleep, to lessen their suffering. I honestly don't understand why a person who is only going to suffer more is not allowed to ask for medical help in ending his or her life.