I had a similar experience after getting hit by a car while crossing the street. A friend who saw me and came running over actually thought I was in shock or something, because he couldn't believe that I was taking it so calmly. The adrenalin also helped, of course - I didn't feel any pain at all until nearly half an hour later. The only emotional reaction I can remember was extreme annoyance at the breaking of my glasses.
Oddly enough, I fall into the same category as the post author. I don't think I'm very good at reacting swiftly, and I absorb information and handle that sort of testing very well. But I do generally manage to keep my head. I suspect this is a pretty recent development, which may affect my perception of the matter.
I've found one useful heuristic. If I periodically remind myself to keep cool and reevaluate the current situation, I generally get good results. Slow-reaction types tend to quickly make a bunch of assumptions when thrust into a situation calling for swift action, and weeding out the erroneous ones is very helpful.
Related to #10, I've found that building up understanding of complex topics (e.g., physics, mathematics, machine learning, etc.) is unusually enhanced by following the history of their development. Especially in mathematical topics, where the drive for elegant proofs leads to presentations that strip away the messy history of all the cognitive efforts that went into solving the problem in the first place.
I suppose this is really just an unconventional application of the general principle of learning from history.