The best thing I can suggest is to excuse yourself and go to the bathroom. Pick a stall, any stall, throw on a pair of headphones, and play the most relaxing music you have for 5 minutes or so.
If some part of this is not allowed at your school (like having an mp3 player or something) then talk to someone and get an allowance made.
If they won't make allowances, then just go see the school nurse instead... every single time you get ultra-stressed. It may suck to do that, but being a polite pain in their ass sometimes can get those in charge to have a change of heart about making that allowance.
If all else fails, get your parental units involved. Being diagnosed with AS means there are certain things the school must allow to help you learn in the most productive way.
Just remember, be polite, clear, and firm in what you need. The worst thing you can do for yourself is become angry. Anger is a sign of weakness. Knowing what you want and what you are allowed, expressing it clearly, and holding your ground puts you in the position of power. The occasional compromise isn't always a bad thing either, as long as you are truly OK with the compromise.