It's an annoying state that seems to have evolved a bit since I was young. I've played violin for years, and for most of those years I've played solo pieces in recitals. I used to get shaky before a big performance (not a good thing if you're trying to draw a bow smoothly), since if you mess up in a solo piece, everyone (or what seems like everyone) can hear it. When I started giving serious class presentations in college, it was the same thing; I had a bad habit of babbling, and made a lot of little nervous movements when I was talking. (I remember specifically being told not to clutch the podium, or bang the pointer stick on the floor.) I also have a tendency to run on autopilot when I get into the talk; to this day I can't remember much about my undergrad thesis defense, other than one or two of the questions.
When I got to grad school, and had to start teaching labs and giving more in-depth talks, I developed the really annoying habit of sending all my stress straight to my stomach. Now, whenever I give a presentation, I can't eat before, and I'll usually keep myself up at night because my stomach is so upset. (This is not going to go over so well with my talk's early morning time - if I don't eat, I'm likely to keel over from low blood sugar.) What really annoys me about this is that I know - and I've been told - that I'm perfectly competent and actually give pretty good talks. Unfortunately, it's one matter to know something in your head, and another to make the rest of your body believe it.
One thing I have found that seems to help is doing tai chi to calm down - it involves really slow, controlled movements and breathing, which is exactly what I seem to need. (It will look really silly if I do that before the GSA talk, since I'm pretty sure they won't have a meditation room set aside.) I also had some fun with the other volcanology students, who helped me come up with an alert level scale for nerves:
Green - Everything's Cool
Yellow - Mild Panic
Orange - Why Did I Agree To Do This Again?
Red - I Am Totally F*cked
What I really hope is that I'll eventually get over this - or, at least, be able to control it much better. Has anyone else found a point in their career at which nerves are no longer such a big issue? What do you all do to deal with the pre-talk jitters?