For the last five months it feels like whenever I run my "internal thermostat" is broken. I overheat and have to stop because I feel like I'm going to faint. This feeling also happens at the gym. I feel lightheaded after only a half hour and need to sit and calm myself. I don't know if it's my diet or what. I think it might be vertigo because I feel like my head is swimming in waves when I stand still and everything is closing in on me. I am 32 years old, 5' 11", 167 pounds, in great shape, and have never suffered any major illnesses before. About an hour afterwards, I feel queezy (though I've never vomited.) Thank God I know when to stop running. But I'm worried and don't know what's wrong. I even feel this way at weddings sometime and at concerts. Thank you for your time.