I had anxiety attacks throughout high school. Thankfully I seem to be rid of them now ( I say that, I'll probably have one next week D: )
My biggest help was to sit or lean against something, have a glass of water if you can stand it, and to remember that they are temporary. "This too shall pass".
I have an anxiety disorder and now that I am preggers I am off my meds. Try deep breathing from your tummy. If your chest is moving you are not doing it right. I think there are videos on youtube explaining it. It works well for me. Also try doing something that distracts you from whatever is panicing you.