What is it about public speaking...

That makes you go from eloquent and well spoken to jittery and barely able to form a coherent sentence?

I had to give a presentation today for my population health & production class, and it did not go well.  Practiced the night before, no problems.  Get up in front of a whole nine or ten people, and my brain suddenly decides that it will no longer be able to keep a straight thought, voice starts shaking, the works.  So frustrating.  It's even more frustrating when I compare it to other things.  When my band was together, playing gigs wasn't intimidating.  3000 people and a bass?  No problem.  10 people and a powerpoint?  Bomb it.  Grr.

I have my 3rd year presentation in December.  I really need to fix this by then.