TONS of great advice on this thread...it really would make a great sticky.
I'd like to take a different tack. I don't think it'll help with the upcoming test, but it may help with the problem in general.
I have some questions for you. It may seem a tad harsh, but it really is not mean to be.
What is it that you are scared of? What is the worst that can happen?
The reason I ask is that I'm getting a lot of anxiety vibe off of your posts. Even the earlier ones prior to the test. I'm wondering if there isn't a fair bit of anxiety around doing these SD techs spontaneouosly. Thus the need to plan and prepare and the lock-up when actually put into position to do so. Basically, I'm saying what everyone else is saying, but from a different perspective.
Here's my take. Long ago and far away I was once in music school. I'm a decent musician and I had a fair bit of promise. Every semester as part of my grade I had to sit for a juried performance. I had to play a few pieces that I'd prepared over the course of the semester for a panel of my professors as well as perform for the entire school.
Inevitably i would get the worst panic attack. Literally get tunnel vision, my leg would shake so bad I almost couldn't operate the piano pedals. My mind would go blank. It was awful.
Now, It doesn't sound as if what you expereince is to that extreme a degree, but it certainly sounds like it's in the neighborhood.
Here's my advice (FWIW). Have you tried something like progressive relaxation? Basically, think about the worst case scenario (perhaps testing) and rate how tense and anxious this makes you feel. Then think of a related but totally non anxiety producing scanario. Thwe worst case is 10, the least case is 0. Then come up with some sort of "relaxation scenario" Sitting on the beach, sleeping in on a Saturday morning...whatever works for you. Also learn how to otally relax your body and let go of tension. A common technique is to lie down with your eyes closed thinking of your relexation place and starting from your toes and working your way up. Tense your muscles and then elt them go...paying close attention to how the let go sensation feels. Very shortly you should be able to evoke this sensation of total body relaxation at will. You can even pick up tapes and CD's where someone walks you through this.
Anyway, once you can relax yourself, start with scenarios 1 (least) and think about it...when you start getting anxious...just use your relaxation technique. Don't move on until you can think about a scecario without getting any anxiety. Work your way up through increasinlgy more difficult scenarious until you can self-relax when confronted your worst-case scenario.
The next level is to try to use this in the actual scenario.
In this case, you are going to teach yourself to systematically relax and let go.
It works great for me and a number of my clients over the years. Now it may not take the anxiety away. I still get nervous if I have to perfrom...but I can handle that energy now and channel it. I'm in control rather than the fear.
Then again...I could be totally off about the root cause of the problem here. Just tought I'd throw that out for you.
Good luck and keep training.
Peace,
Erik