First, I agree with the confidence and control crowd. One thing that helped me was attending some camps where people who know what they're talking about validated my abilities. That has helped my impulse to hurry and get the game going again before something bad happens and I look stupid. It may well take something else for you, but that's what it took for me.
Second, is the faking it part. I have spent a lot of off court time repeatedly thinking through how I want to handle things. I have done it enough now that when I call a foul, I just act out the script I have rehearsed. I pause, make my signal, take note of the foulers number, the shooters number, and calmly call my partner my name and say how many shots we'll have. Then I hustle to my spot, pause while I come to a complete stop, and signal to the table. This mental rehearsing helps me a lot in situations where I really am not that relaxed...at least I have practiced how to look like I am
