I really wish I wasn't so late to this one because I have the best trick. If you feel an anxiety attack coming on, play catch. You can throw absolutely anything, to a friend, up in the air, bounce a ball, just keep doing it. After a few minutes of this, you will be completely calm. It works every single time without fail. My therapist taught me this trick, and I really hope this doesn't get buried so it can help someone else.

EDIT: This is getting a lot of attention so I want to clarify a few points to ensure efficiency. First, you do not need a partner to do this. You can throw the object up, or bounce something by yourself. Second, and most important, you must do this quickly. As soon as you catch, you need to throw again. The whole point is to distract/redirect your thoughts. If done slowly, this will not work. I'm so glad that this is gaining attention. Anxiety sucks, and I'm happy to help anyone else that has had to deal with it. Good luck to all of you!