Like EstherDoll says, how many of us know what concussion is or what the symptoms are? Lots of people think concussion is being knocked unconscious, for example.

I was watching some videos on youtube about concussion in sports, and how many people weren't being diagnosed because they simply did not know the symptoms. Someone may not volunteer they have blurred vision because they don't think it's relevant.

And also, the doctors didn't know the symptoms either.

They found that after teaching the participants and doctors the concussion symptoms the diagnosis rates shot up because the doctors were asking the right questions, and the sports participants knew what symptoms to look out for.

I spoke to a nurse at a head injury charity, and she says it's possible for someone to have no symptoms at all after their event, but develop really debilitating lifelong symptoms, even if they are subtle they can be life changing.