It's really no different from telling a cop who pulled you over that you're strapped. "I have a legally concealed weapon, I'm a permitholder, I don't mean you any threat, if I'm going to be put in an ambulance or put under heavy pain medication it might be best if we have a cop hold it, or you might have a secure storage place in your ambulance."
Basically, don't let THEM find it, be cool, let 'em know you're not hostile, it's all good. You WILL get it back unless you really screwed up (like, say, this is a DUI scene post-crash or something).
The REAL tricky aspect of this is if you're either prone to diabetic crashes that make you look drunk, or an epileptic. THAT, you have to really be careful with. But if you've basically got your wits about you, shouldn't be an issue.
Hmmm.
One more case where it can get tricky is concussions. We have recent video of somebody who was concussed but despite that, managed to handle himself fairly well, including continue with his job: Conan O'Brien. Check this out as it's actually on-topic to the discussion:
http://www.bittenandbound.com/2009/0...injured-video/
Look at what he was able to do despite taking a serious conking and not even remembering most of it afterwards...yes, the whole thing is worth watching. If you KNOW for a fact that you need to tell medics politely that you're legally strapped and will let a cop or medic disarm you, you should be able to pull that off despite at least a moderate concussion. At some point of course even that much will go out the window, but at the same time I know of no concussion victim who has ever gotten deliberately violent with weapons due to a conking.
Random flailing of arms, well yeah...that can happen...