Public Speaking Makes Me Want to Barf

I promised more on this subject so here you go.
At the end of every Mops brunch we have a sharing time. I call it the "Kiss and Cry" time. Really, it gets sappy. I try to avoid it altogether. It makes me uncomfortable. But this time I had to say something. Now that you've read the last post you have a little perspective on what I said. It went like this:
"We always get a bunch of cards from our friends at the end of the MOPs year. I am amazed by how many said I was strong. I'm not really. I'm a mess. But through the grace of God I can be strong enough.
All of my best friends either came from MOPs or I drug them to MOPs with me because I believe in the program that much.
This year I was struggling with some rough stuff. My friend had to literally hit me over the head with the truth. The truth that I didn't want to face. But as my friend she has earned the right to tell me things the way they are.
My hope for you is that through MOPs you can find these kinds of friends. The kinds who know your heart and love you anyway. The kind who think you are strong and help you become that."

My voice was breaking. I was sweating, and near the end I was in danger of crying.

Why? Why can I sing a song and not miss a heart beat, but speaking about myself in a transparent way makes me want to barf? Even typing these kinds of things gives me the shakes and the stomach wobbles! Why?