Not the most physically painful, but definitely one of the most unique pains I've experienced was the electrical stimulation on my vocal chords to get the paralyzed one back up and running.
Basically they jammed electric needles into my voice boxand wiggled them around while I making me say "Aaaaaa" over and over again so they could watch with a camera in my throat.
So that was fun.
And when I say "wiggled around," I mean pretty strongly. Like, grab your voice box and wiggle it around. That, only with needles.