While Standing For A Few Minutes ,I Felt Suddenly Nauseous.

while standing for a few minutes ,I felt suddenly nauseous. I sat down then I got a hot flash raising from my feet , then I turned cold , then everything in my body got painful. then I saw tunnel vision with an extreme headache then others around me said I turned very white, my eyes rolled in the back of my head and my head slammed down on to a counter. I don't remember blacking out and next thing I knew people were calling my name and holding onto to me trying to keep me up straight. I don't remember blacking out & didn't remember losing any time at all. I thought everyone was making it up. I then got really nauseous & had to go throw up , this happened last night and I still don't feel right today.