Why would a 21 year old female be fainting like this?

I am a 21 yr old female, weight 175 (lost 30 lbs or so in the last 8 mths) height 5'4". I have been going through "fainting spells". i p out for just a minute or two and then I wake up and I throw my guts up, get some fresh air and a cool rag and i am ok. It happens once every few months. Its hard to explain how I feel before i p out, all I can say is I just feel WEIRD! My ears have been ringing overwhelmingly for about a month now. My pulse rate has been low (consistently) for months, I had a FULL cardiac workup at our local ER and they said everything was fine! When I p out it doesnt have ANYTHING to do with standing, sitting, etc. It has happend sitting AND standing. When I do p out I get short of breath (not hyperventillating just short of breath), I start to feel like im dying... period... i feel like im leaving the world.. then I p out I come to and Im sweating, my husband says my face is as white as snow, my heart rate is low, my ears are ringing, i just want to sleep i dont want to move, i throw up, my husband keeps a cool rag on me and then Im ok. The last time I full on ped out was in October, that night I passed out, came to, and then passed out AGAIN! But the difference that night was I passed out twice (didnt happen before that and hasnt happened again) and I didnt vomit that night. I have checked my blood sugar when I passed out and it was perfect. I dont like feeling like this, when I pass out (or almost pass out) I feel weird for anywhere from a few days to a few weeks after. Has this ever happened to anyone else??