I had this problem three years ago- came on suddenly and though it was bad enough to head to the doc, he found nothing, but wanted to keep monitoring me. Being really our of breath at the end of each pass was the only symptom. At some point, I was exercising on a machine with a heart monitor and found my heart rate never rose much above my normal resting rate. That got his attention, so he ordered an EKG and a day later I had a pacemaker. Before I was released, my wife asked the hospitalist what would have happened if I hadn't gotten in. His response was " Um, er, uh, that would have been incompatible with Uh, um, er, uh, ... life". So, while you're probably fine, don't take chances- you're concerned enough about this that you're posting at 2:32 AM, right?