alandeis1985,

First off relax !! Its just a procedure and not a valid one.
Now that your breathing easier, download the "Lie Behind the Lie Detector" TLBLD from this website, read it, go straight to chapters 3 & 4 and understand what is about to happen to you. You can do the first 2 chapters later after the interrogation (test).  Once you understand the procedure and the game, you will know what to expect and your stress level will diminish. As the polygrapher really wants you stressed, it will lower that fear and Anxiety. Your choice to use countermeasures is personal and how you handle it is up to you. Go into the test with knowlege and a great game face. But do not under any circumstances let on you have the knowlege you do. It will certainly be a failure for you. 

You will be successful & good luck.   

Regards ...