Light head and dizzy when working out...?

Has anyone heard of this or have this happen?
(When I be active) I would be running or doing something causing me to breath heavily built, mostly through my mouth. My chest would get tight foreboding and my trachea felt resembling they were swelling up...approaching asthma.
ALSO...
When I wourk out or do any physical activity I find light head and dizzy. The Doc says my heart looks moral and I had a stress oral exam. What the heck is going on with me?Light head and dizzy when working out...?
There is asthma cause by exercise, also are you hydrated when you work out? See another MD to get answers.
This may be what is going on:
http://www.discoveries.typepad.com/...