Death Throes. Its a 5th level Clr/Sorc/Wiz in the Spell Compendium, reprinted from the Planar Handbook.
It's too high level to make a potion, but you could make a single use Wonderous Item that you consume like an Elixer. Label it as Featherfalling or Waterbreathing or something else you kinda need to have faith in that it'll work when you use it. Hillarious.
there's another spell called Phoenix Fire from Book of Exalted Deeds, does a crap ton of damage by making you explode, die, then resurrects you the next round 1 level lower.