lol, exactly what i was thinking shimmygirl.
depends on the spell really. let's say you have a real working death spell, if your intent/hatred is strong enough, you've charged enough energy and focus well, then, yes, i do believe a curse could cause death. but i think this is a rare occurrence. normally the person will become really weak, and wind up seriously hurt form a curse, but death i don't think so, unless you're skilled enough at curses.
also, the spell needs to be a working one. i collect spells, about 98% are working spells, but when i come across ones that are hillarious, i keep them as well. so i've seen my fair share of death spells that are like 'say "die" 27 times and they'll drop dead' or 'write their name on some paper and they will die.' obviously these will not work, but there are working death spells out their.
onto using it on yourself, on the up side if it backfires you'll still have some result, but why would you is the real question. if you got a working death spell and you actually tried, like conjured up enough rage and energy and focused, it would work. while i'm not saying kill yourself, there are easier ways, like a knife. [it's a joke, i'm not seriously telling you to do it] so, in conclusion, if you cast a real death spell on yourself, you will die. if it backfires, i don't know if you would die, or get badly injured and suffer for a long time as a result. [because from what i've noticed when a curse backfires, it backfires bad]