I also have a brand-new prescription for gunfire jitters: When the shooting gets loud, proceed to the nearest wooden staircase. Run up and down a few times, making sure to stumble at least once. What with the scratches and the noise of running and falling, you won't even be able to hear the shooting, much less worry about it. Yours truly has put this magic formula to use, with great success!
Anne Frank (ed. Bantam Books, 1995) - ISBN: 9780385426954