Nearly passed out at the post office

I just had the scariest thing happen. I was at the post office at the window and I was a little nauseated, but what else is new. I was wearing a warm jacket and started getting hot. Then I broke out into a drenching sweat and my vision got dark and I thought I was going to pass out. I finally finished and I sat down on the floor because I couldn't make it to my car. I immediately felt better, but had such an adrenaline dump I was left shaking. Any one else have this happen 10w6d with my first. It was so scary!