Do you have to be knocked out to be concussed?

It is a common fallacy that you have to be knocked out to be concussed.  This is not true.  Concussion can follow an injury with loss of consciousness, but can also follow injury where the victim has remained conscious throughout.  It is therefore probably a lot commoner than you might suspect, but because in most cases you will recover with some rest, you may not appreciate that you have been concussed.  If you have ever fallen off, hit your head & felt a bit woolly for a few hours afterwards that was probably a mild form of concussion.