When I used to race MX I pinched my sciatic nerve. Absolutely the worst pain I've ever felt. Searing hot knives up and down the back of my leg from heel to lower back. Absolutely unbearable. I found out later I was bending my foot pegs, so coming down from 20ft not landing flat on your feet had some nasty effects. Was gone in a few weeks after I straightened and re-enforced my pegs, but wrong word that was brutal. I'll never forget it.