Having experienced a couple of concussions, and having read a lot about sports injuries of this sort, I can provide some perhaps useful details.

Detail No. 1 is that every "concussion" is an individual event. The symptoms and consequences of each one are not entirely predictable, or even diagnosable at the time of injury. Many of the consequences don't manifest themselves until much later.

My most recent incident of this sort happened several years ago. I slipped on black ice in the parking lot of my local grocery store, at night, while carrying two large bags of goods in my hands. Direclty backward, no chance of catching myself, landed on my shoulders and the back of my head. I never lost consciousness, but I literally could not move for maybe half a minute. A bystander saw this happen and rushed over to help me, and asked me questions, and I could not respond. It was, I suspect, much like a lot of boxer's knockouts. The ref could have counted to fifty or more, and I would have heard every number.

After about half a minute I managed to struggle to a sitting position and was able to respond verbally. He helped me to my feet, and I leaned against my car for a minute or so, while he collected the goods that had been scattered across the parking lot in the fall. I think he was about ready to go get medical help when I convinced him that I was okay, thanked him profusely, and could drive home, which wasn't very far away. In retrospect, that was probably a bad idea; I should have had somebody look me over. I did get home, but had a significant bleeding cut and swelling on the back of my head, which alarmed my wife considerably. I went directly to bed, and was both dizzy and slightly nauseous (although I didn't vomit).

For the next three or four days I was unusually sleepy and lacking in energy. Stairs were a bit of a challenge, especially going down. Eventually it cleared up, and I never did see any medical people about this incident, but I doubt I would have passed an NFL concussion protocol, unless I played for the Seattle Seahawks.

A pro sports incident that has always kind of haunted me happened in Major League Baseball five or six years ago. A really fine player named Justin Morneau, who had won a Most Valuable Player award a couple of years earlier while playing for the Minnesota Twins, was struck in the head by a defensive player's knee while attempting a slide into second base, on a routine infield grounder play. I've seen the replay of that incident numerous times. It didn't look like much, and certainly wasn't intentional. But Morneau missed more than a year of playing time, in the central portion of what should have been his most productive years, because of concussion symptoms. You don't want to stand at the plate and face 98-mile-an-hour fastballs if you can't focus your eyes and feel like you're about to fall down. Morneau never recovered his all-star abilities.

And, of course, we now know the effects of multiple concussions are cumulative. Stories of punch-drunk boxers who can't enunciate clearly are legendary. Medical evidence of severe brain deterioration in NFL and HHL players is well-documented. Some of these players have, tragically, known about this. The great NFL linebacker Junior Seau, who had a really good gig announcing and starring in feature shows after his playing career ended, shot himself in the heart, so he dould donate his brain to the medical people for study of the syndrome.

Concussions are serious injuries, and every one is its own thing. So, for your writing purposes, you have leeway to make your concussion have whatever effects you need. But they are significant injuries, in any event.

caw