I haven't been in that many emergencies, though I try to be prepared for them (getting some training - a bit out of date this year though - and keeping supplies on hand).
The times that emergencies came up, the difference in my reaction was how clear-cut the situation was.
When my daughter choked on a grape at age 2, I whacked her on the back and it came flying out before I could think about it. The whole thing was over in about 3 seconds.
When I heard cries from next door, it was much less clear cut. First I wasn't sure where they were coming from, and then I couldn't hear well enough to know if my help was needed or wanted. I did intervene, which turned out to be the right decision, but it took over a minute to act. (My neighbor had a heart attack and his wife didn't think to call 911, in her panic.)
I have enough of a sample to be pretty sure of how I tend to act. If it is obvious what the problem is, and that it is urgent, I act immediately, and maybe freak out later. If it is not clear what is going on, I hesitate until I understand the situation.
Of course I second-guess myself afterward, and think of things I should have done differently, but I am pretty sure everyone does that. I've had firefighters tell me they sometimes do the same, and there aren't too many people more trained for emergency response.