Kathleen, it sounds like hyperventilation, which results from stress. You could Google the condition, as I'm sure that way you will find a more lucid explanation than I can give, but basically you end up with not enough carbon dioxide in your system (we do need the right balance). There's a trick you can do with a large paper bag, if you can find such a thing. Scrunch up the top of the bag and exhale into it. Then breath in the 'stale' air from the bag. Do this a few times and it should help.
JP x