I has never happened when I was pregnant, but I have felt like that sometimes. I have actually passed out from that. I did feel that way when I was in the hospital delivering my twins. It could be your blood pressure dropping, which will cause your heart to race. My blood pressure fell really, really low and my heart was racing up to 175 bpm. I would definately make an appt with your doc. Can you see the other doc, not the one you called? You definately need to be seen about this. I hope you can find something out soon, hun!