I know exactly how this is.
I used to do BMX bicycling and i would go off the craziest jumps you've ever seen. Some of them nearly approaching verticle.
Then one day i just couldn't go off them anymore. For some reason I was just scared to. No idea why. It took me till i was 13 to be able to do it again. When i did, it felt very liberating.
It's funny that i was just reflecting on this experience right before i saw the thread. Maybe there ARE no coincidences *x-files music plays in the background*