If you freak out take a second to breath, don't lock your knees, think before you speak to reduce the umm-age, drink plenty of water to avoid cottonmouth, stretch your jaw out before it, it helps you speak clearer. If you know any vocal warm ups you can add those on as well.
Bring a bottle of water up there, if you blank out, drink from the water, it will make it seem like you are taking a drink and didn't forget what you were saying