There was that guy that did rocket sled testing the worst he had was detached retinas. John Stapp
If I'm not mistaken, breaking the sound barrier through free falling would probbably be faster and more damaging than rocket-sledding.
If he's in free fall, there is air pressure, nothing to grab a hold to, no way to cover yourself from the wind, and lots of other things.
Detached retinas doesn't sound too good either.