Surprise Tests; how do you manage them?

Surprise Tests; how do you manage them?

I freeze. Solid. Any and everything I ever knew becomes a Ninja; an expert in stealth.
Nothing will take the fear away. I've tried deep breathing. (Actually, this will work if the test isn't timed; if it's timed, I can't stop thinking about the clock.)
I've tried diving in; not recommended, the answers don't start flowing until the clock stops ticking. All that happens is I become a cry-baby; blubbering, tears refusing to remain behind my lids leak out.
Why?
I KNOW my stuff! I'm damn good at it! Responding should be easy, right? Yet put me on the spot and all my confidence shrivels up and evaporates; I question my own existence!
As you may have guessed, I was put on the spot earlier this week. I fear I lost a lucrative opportunity. I know that people will respond with: but, what if something that isn't supposed to occur, occurs? How will I manage that?
Trouble is, in an emergency I'm stellar. (No, I'm not bragging, it's not bragging if it's the truth.) I don't collapse until the immediate danger is over and everyone is being taken care of. (Yeah, I've had a fair bit of emergency opportunities...) but bring the press in and shove a mic in my face and all you're going to get is a red-faced person, sputtering nonsense; surprise tests.
I almost always had to do a makeup test in school; unannounced exams just terrify me. Spiders too. I wonder if they're related...?

~khrys