What is happening is not real. That doesn't help to know that although it should. So, you must treat it as if it were real.
Use a vaporizer - stick your face in it and let the stream go in your lungs
Use an inhaler - any kind
Distract yourself. I had an attack last night and I went in the chat room and babbled for 10 minutes and it went away.
This is a classic panic attack. If you can get a scrip for small dose Xanax or similar, it will help. If not, then try any of the Holistic stuff. It helps your brain to quit agitating you.