Hi there!
Its so weird, yesterday I was thinking about the same subject! When something real happens, I am calm. Like last week for instance, four horses got loose and were running around the stable yard. It was just me and my instructor trying to catch them. It was a very dangerous and stressful situation but I was so calm! And at work when the cash register crashes, I dont' panic at all.
I think this is because we are momentarily distracted from ourselves and realize that someone on the "outside" world needs us. Also, maybe we "practice" so much inside our fight or flight response that when we actually have a situation where it is appropriate to use it, we know what to do!! :)
LOL
Jen