That's called adrenaline. It's why couch-cowboys who buy a gun, or a knife, or a baton think they are just going to "see red" and be able to perform. Doesn't work like that. Your fine motor skills go to shit. It's why a sport like BJJ, even if you are not any good, get you to experience having other people put their hands on you (and try to strangle you) helps inoculate you to some extent. I've never been mugged, but I was in think brush and was charged by a very large, very angry boar. I don't remember clearing my pistol, firing, and most certainly missing each and every shot at almost point blank range. Luckily he ran right past me. But I get it. The shakes last for what seems like an eternity.
What's the expression - you don't rise to the occasion, you fall to your lowest level of training/preparation. As a gun guy, I'm talking to all you other gun guys.....adrenaline is a motherfucker, and @Gatorubet you did well thinking on your feet like that. Use the hose. Douse everyone and everything. Don't try and be a hero.