I don't have much fear of public speaking myself, but I'll guess that the answer to your question about audience attention depends heavily on whether they're paying / not paying attention (1) from the outset for reasons that have nothing to do with you, (2) from the outset because of your reputation or appearance or something, or (3) as a result of what you've said and done so far. I would expect a public appearance to be maximally traumatic when everyone is initially paying rapt attention, but as you proceed they visibly get bored and stop listening.