When you get very anxious, you tend to take short, shallow breaths. Be mindful of your breathing and take deep, slow breaths and that will help instantly to calm you down.
What I had heard from books and other people is that the breathing you are speaking about is called hyperventilating. I recall my mom being too slow in her breathing so she could breathe normally. I also recall there was a time, when I used to be a teenager, my mom was advised to get a lunch bag and breath into it.