Same thing happened to me in a Pitts only I was wearing a helmet and didn't feel it. But I wrenched my shoulder and was in pain for weeks afterward.

I wasn't flying it at that point so was taken by surprise. Took him by surprise though, when I fell out of a roll into a spin.
Aerobatics is like being beaten up sometimes, sore heads and pulled muscles.
Sadly only flying boring old 172's and 150's lately. sigh!!!!
PERK THE RV8!!