When i run my legs go quite numb, ive fallen over because of it where i simply cant run any more. and i dont even have trouble breathing , just my legs go numb and sometimes i get pretty shaky.Ive had chest pains before but no doctor knew what it was. Also when i run up my stairs at home, im so out of breath and my legs go funny again. I always thought it was just something to do with my asthma so is it ?