I am a professional dancer and in class or rehearsal I need to go to my knees at times.  My blood pressure drops and everything goes white. Then my heart rate speeds up and I get the cold sweats. I was told by my Dr. I am most likely not drinking enough water, have low potassium and iron. I have had an ECG and I wore a heart monitor for 6 weeks. They did not find anything wrong. I am not sure if he is right, but it has been happening to me for ten years. It is very scary and I am afraid it may happen on stage and I will have no choice but to push through it. My family tells me this is not normal. Does this sound normal or common? I am not sure where to go from here because no one seems to know the problem. Should I continue dancing or is this dangerous?