Guys, concussions can easily happen, they nearly happen every football game. There is a reason why the NFL is fighting this so hard right now, if it were to come out that guys are really supposed to be out for about 2 months after every concussion, where there can be guys that will come back within a week or two in the NFL, then it would dramatically change the whole game.
I'll use wrestling as an example, look at that Randy Orton match he had with RVD for the IC title. Orton got a concussion shortly into it, than worked through it for another 15 minutes. He didn't take time off. To go further back, look at what happened with Bret Hart. He had a big concussion from that Goldberg kick, but he worked through it for another week and got a whole bunch of "little" concussions, somewhere around 10-25.
If what Nowinski and his people are saying is correct, it's the fact that what people use to think there were minor concussions that you could could just recover from in a week or two, it's not the case. You might need up to 3 months of recovery time. I'm glad in a way that Nowinski's wrestling career ended, because he can do something important on a whole. Not just for athletics, but for everyone.