"Yeah, I caught a knee to the head in aikido last week."

"Ouch. No concussion, I hope?"

"Nah, I've just had occasional headaches."

"Uh, that's a concussion."

"Oh. Huh. Guess it is."

One of many reasons it's healthy for me to talk to other people. It's been a bad week for getting clocked in the head--today I got a knee to the back of the head, and then a foot to the face. It's all accidental--if people were trying to hit me, I would either have stopped them, or it would have hurt a lot more.

I'm inspired to look at more information about concussions, though.

Most people get better after a concussion without any permanent damage. People have signs of concussion for weeks to months. Repeated concussions could cause permanent damage. After several concussions, your doctor may talk with you about changing sports.
Heheh. Now, the way *I* recognize a concussion is by nausea afterward, which was very noticeable the one time I dropped a steel shelf on my head while working on an indoor construction site ("How??", you ask? because I'm a fucking moron, that's how). Unfortunately I also got nausea when I hyperextended my ankle a month or two ago, and I don't get concussions very often anyway, so maybe I just sort of discounted it. Maybe I shouldn't do that in the future.

For the record, there's a fine NIH page about concussion symptoms and first aid, and the University of Missouri has some biological details.

Take your hopes. Take your expectations.
Take your desires, your wants.
Make a list, if it helps.
Lay these things down.
Take your hopes and expectations and lay them down next to your fears, your insecurities.
These are all the way you wish things were, not what they are.
Be free of wanting,
You brought it with you;
Now put it down.