You've posed an interesting question, and one that I'm sure many people have pondered before.
I think that there's several different layers of actual fear. For me, here's a few:
Fear for my children: This is my strongest fear. I find that there's always an underlying concern that I live with daily when it comes to my kids. My daughters are pretty young still, so it's more of the concern for their health and welfare, security and piece of mind...that kind of thing. My oldest daughter almost lost her life once, and that kind of fear is undescribable. In that particular situation, my need to comfort her and help her fear surmounted my own fear. I became very calm, knowing that would help her the most. My head cleared completely and I was able to concentrate on what HAD to be done to save her life. I don't know what caused this reaction, either it was God laying his hand on me and giving me strenght or my primal need to nurture and protect...probably both.
Fear for my life: This has only happened to me twice; times when I was actually in true fear for my life. If you're coherent, and concious...your primal side takes over and you'll fight back. That's what I did. There was a moment when I was frozen solid in fear, but something inside snapped and my fear was forgotten completely along with any pain that is involved in fighting for ones life. Unfortunately, I can't explain that reaction either.
My fear of spiders: Seriously, don't laugh! (lol) When I was two, I got stuck under a house in Florida (where spiders are the biggest, nastiest creatures that walk the face of the earth) and they were all over me. I remember it with clarity unmatched to any other memory I have. Now, I have serious arachnophobia. I can't even look at the little buggers. The way I deal with that fear is totally day by day. If I find one in my bed, I won't sleep in my bed for about a week. If there's one at work, I *demand* that my supervisor kill it and/or dispose of it! (he's wonderfully tolerant of these little episodes) All in all, I just have to try and put the fear out of my mind so that I can function properly.
I'm sure this all didn't help much, but I hope it shed some light. I think dealing with fear is totally subjective. The ways that people deal with their fears is as different as each individual's fears are to another person. The key is finding out how to deal with yours best, and only you can do that. I wish you much luck in this, and you have my thoughts.
May I never be too busy to help another's load,
Then I'll be drinking from the saucer 'cause my cup has overflowed.