hello, thanks for the opportunity to ask something i've always wondered about. first i would like to say that I've had physicals and blood work all through my life and results return very healthy and nothing shows wrong with my heart. my back ground i'm a prior marine and very active. i run an average of 25 to 30 miles a week lift weight and even swim several miles a week. and have for years. but i'm prone to gassing, thats what i call it , a complete shut down of my running or swimming, especially on short races like a 5k. which i know i push hard. at times. i may take off to fast at first or sometime in the race but if its going to happen it usually happens somewhere in the beginning of the run. all is well then all of a sudden i get soft pressure high in the middle of my chest and i can feel almost hear the sound of my heart and its all over , i'me totally gassed, done , spent. the race is over. i may have this pressure for hours after the run. one time till the next day , not painful just weird feeling , till it goes away i'm completely spent of energy what happens to me.?