I was in a "real" combat zone (though some 20+ years ago) and nearly always find others impressed by my relative calm in almost any circumstance. Very few technical situations even come close to competing with bullets whizzing past you and mortar shells exploding. So I feel I'm pretty prepared to deal with any situation us "normal" people deal with.
However, like Karyn, even though I was a "combat medic" (meaning I was given a little medical training beyond what the rest of us "grunts" were given), I had a professor in one of my first college courses collapse from a heart episode (not a life-threatening heart attack, but more of a blood flow issue), and I was somewhat frozen. I had the sense to instruct a bystander to call 911, but I was far from the first to rush to his aid, even though I was probably as qualified as anyone (I was only about 6 months out of the Army, at the time) to get to him.
Fortunately, he was OK, but I think all of us have some situations where we're more qualified than others. I've found myself feeling less qualified in medical emergencies (beyond the one above) than during "critical" systems circumstances, even when they require complete focus for 48 hours or more.
It is interesting, but I know I can at least keep a calm enough head to get the right people in place, even when I'm not the right person.