Surgery recovery, too. An older cyclist is going to need surgeries more often than a younger one, and will take much longer to recover. For some guys a high-end electric assist bike is how they stay riding with the A-group while they're recovering.
I had the same thing happen once, and it was as fascinating as it was unsettling. Very slight movement of one needle in what seemed like a pretty inconsequential part of my body produced a near-instantaneous full-body reaction involving many systems.