I'm guessing something like e.g. Alzheimers or some other quality of life degrading, but not lethal, disease that makes life (not as) worth living, at least pas

I'm guessing something like e.g. Alzheimers or some other quality of life degrading, but not lethal, disease that makes life (not as) worth living, at least past a certain point in the progression of the disease. But because its not lethal, it won't take you out of your misery.