OK.im 14 and when i go exercise(jogging or other vigorous activity), sometimes in every week or so, i get what feels like a heart attack . just to be sure its a heart attack, i get very lightheaded, i feel like im breathing in a plastic bag and no breath is helping, and my heart is POUNDING really fast and i feel it in my head. there was this one time when that same thing happened, only i think that it somehow stopped because my heart slowed down by A LOT and i felt like i could breathe again. so...... 1. if these are heart attacks, what could i do to stop them? -or- 2. if there not heart attacks, what are they and what could I do to stop those ?