I had a very similar experience on my first tandem jump in Hawaii. I could not catch my breath as soon as the freefall began, I tried hard to force a breath in and out, but the air would just not move through my nose or mouth. I was not nervous or scared at all so I know it was not a panic attack, I LOVE the adrenaline rush but I simply could not get the air into my lungs. Once the chute opened, I was able to breathe normally again. I had the same breathing problem in an indoor skydiving wind tunnel; I think it has something to do with sinus problems or sinus anatomy... It totally sucks because I love the thrill of skydiving, this breathing thing is such an awful side effect. Hopefully someone will come up with a solution!