It happens. It has to me. Only once, only a dribble of pee, but, yep. When something happens to my computer, and I can't fix it, and I'm afraid of losing my best friend, who lives in Britain, with me all the way in America, or, I'm afraid I'll tick off the person who fixes it, my bowels want to move. When I can successfully fight them moving, orgasms have happened, instead. It's just the adrenaline.
Fear causes 3 responses, fight, flight, or freezing. In a lot of situations, you'll fight, or run. I have CP. Me, fight? I'd be killed for trying. Me, run? I can't walk. Freeze, that's me, most of the time, unless I can make my words a weapon. Sometimes I can.
It's a very short trip from the mildest bad thing ever happens, and I think, "I'm dead; I'm dead; I'm dead; I'm dead; I'm dead; I died; I'm dead!"
Downright scary parents as a kid.
Now, what good does a frozen animal do for itself? It poops or pees, so it's less apitizing to whatever wants to eat it.
When would someone without a disability freeze and go? On a roller coaster, what are you going to fight? Where are you going to run to? You can't do either, from inside that ride.