Thanks for all of your advice. It was all very enlightening. Actually, I have been diving for about 15 years now and have never had any difficulty with my breathing apparatus before. I have had a few nervous moments ie: where's the boat? rising too fast. Where is the exit to the cavern? I really thought for a moment for the first time using scuba, that my luck had run out. First there was such a feeling of surprise. Why was my regulator, which had always faithfully provided me with air, doing this to me? Then a flash of fear and adrenelin surge as I began gasping. Then the sole thought of, must get to surface as soon as possible. The fact that I was in shallow water was a great comfort, knowing that I might be choking but I would make it to the surface where I could work it out in an open air environment. If I had been deeper, like below 30 feet, I do believe I would have begun to panick enough to race to the surface too fast or spat out my regulator and draw in even more water. That feeling when your airway closes is just too terrible to endure for very long without panick when you are at the surface let alone submerged underwater without immediate access to air around you.