I've just realized this. Of all the FPSes I've played, they all seem to have a total disregard of this aspect. You'd think if your character took a shotgun blast to the face and was down to 10% health, you would have trouble seeing, aiming, and walking around. In a game like HL2 or UT2003, you move just as fast at 100% health as you do at 10% health. The only thing I've seen implemented to address this issue was the implementation of "temporary deafness" in HL2 and the BF2(only played the demo) when you're too close to grenade/tank/explosion. (I'm not sure if temporary deafness was used in any FPSes before these two.)