In the UK its finding a suitably qualified medical type who is willing to put his signature on a bit of paper thats says in his opinion your fine.
Its basically bum covering. None of the doctors want to be the one that signs you off. So they just keep on asking for tests which they hope your going to fail.
You just have to wait until they run out of excuses not to sign it. But you may have on going additional checks for years until they get bored of them as well.
Be warned though any hint of any type of fit or period of unconsiousness even with a valid excuse will make them pull you medical even if it happens 20 years after the event.
The trick is to find a rugby playing Neurologist they seem to have a slightly different view on concusions to ones that don't play contact sports.