"To agree to do the speech or not..."

The moment has come when I’ve been asked to do something that fills me with abject fear and would require throwing out all my safety behaviours. I know the answer is in me not out there but i don’t know which voice it is! I have been asked to speak at a large gala dinner early next year. It will be late on in the evening (already I am uncomfortable at that part alone!) in front of 300 people and all my colleagues. About 12 years ago I had a panic attack on stage during a work presentation- my first ever panic attack. So here I am having learnt so much but still none the wiser it seems. Do I want to face this fear (or see the fear for what it is) or do I want to learn the art of saying no to something that will bring about weeks of discomfort and sleeplessness to please others? Which lesson needs to be learnt and how do I find my wisdom?