Yesterday I met with one of the women I'd offered a free 45 minute consult, and we were discussing the nervous symptoms she experienced whenever she spoke to large groups. Although there are numerous theories about why we experience these things (sweating, heart pounding, knocking knees, etc.) - the most common idea is that it's perfectly normal adrenaline that some of us who love the spotlight interpret as a rush and others of us who would just as soon remain in the "shade" interpret as fear.
I think the experience is profound and physical for all of us, especially in this technologically advanced era, because when we stand up to speak we are totally unequivocally physically there. We're not coming in via phone, or email - all eyes are focused on US. We know it, and it's unnerving. I think the fact that we are, by virtue of standing in front of these people, asking for their undivided attention calls into play our own ego issues. Do we really want their undivided attention? Do we deserve it? Do we like it? If we think the answers to these questions are "no" then we're a big ol' bag of nerves. If, on the other hand, we KNOW the answers to these questions are a resounding YES, we're a gigantic bundle of "let me at 'em".
If we know we've developed a presentation with our audience in mind, we know we're about to address some pressing issue, problem or concern, we know we're then going to provide them with a bullet-proof solution, what's to be nervous about? They need what we're there to tell them. We absolutely want their undivided attention. We absolultely deserve it, and (believe it or not) we will like having it. Now the physical symptoms we feel are more like the rush than the fear. It's all in the focus.