This hasn't happened to me in a long time because this last week was the first time since 4 years ago when I was in soccer that I have really been running. It used to happen when I was in soccer all the time though. I just want to know what it is. I get really short of breath and feel like I'm going to faint. It hurts with every step that I take worse and worse. I can tell my heart isn't pumping enough blood through my body because my legs start going out and I have to lay down to get my circulation going again. Am I the only one have this problem? If you have it and have been to the Doctor for it and you have a diagnosis for what it could be, please tell me! I hope it isn't serious!