I had a fear of public speaking when I was younger.. I would sweat, shake, and mumble, and my heart rate felt like it was playing a drum solo on my throat.
Eventually, being forced to do it so much in school, it was just something I dreaded.. which made me annoyed and angry that I had to do it. Which motivated me to get up and get it over with by volunteering first (as I noticed that I could never remember who went first) and I realized that my fear was more freezing up and saying something stupid than it was of the people looking at me themselves. So, I got over it by practicing what I'd say before I said it. Not caring about the opinions of others made it a lot easier to get over that fear.
My fear of heights... I have a love/hate relationship with that. Few things get my adrenaline going more than heights do.. but the physical reactions I have to it are something I have been unable to control. Vertigo is something I get pretty badly if I am not in an airplane, and I've gotten dizzy and nearly fallen from a pretty extreme height during military training from the condition. Being up high is the most beautiful thing I can think of.. seeing everything from up there is amazing. If I could get over the urges to vomit, and the vertigo, and the weakness in my limbs, I think I'd be okay. I've rationalized it all day long, but without much success in application.
I suppose it helps some to rationalize it.. I CAN do things from up high. I can climb a ladder again, I can repel, do some indoor rock climbing, fly, and complete necessary army training. But the less safety features there are the worse it gets. I am unable to get to the top of the rope climb even though I am perfectly capable of doing it theoretically, and I cannot touch skydiving with a ten foot pole.. Roller coasters still give me trouble. I had to turn down an opportunity for air assault school.
It's a work in progress..