i get that and find breathing into a paper bag and then trying to sip water (if you start choking obviously stop and breathe into the bag again) are the only things that can slow my breathing down so that i can eventually stop it altogether. just remember that it IS within your power to stop it, that you've done it before and that you can do it again. also, have you tried bach's rescue remedy? it's a natural remedy that's meant to calm you down, a lot of people seem to swear by it. it comes in a little yellow bottle, you can get it from most chemists.