8 weeks pregnant, almost fainted at nail salon

TheFutureSchoenfelds

I just came back from getting my nails done. While sitting there for the last top coat I suddenly felt off balance. Then I started getting hot, my heart started racing / pounding and everything started to sound distant. I took a few deep breaths and as quickly as it had started it, it stopped. I absolutely felt like I was going down any second though. 

Has this happened to anyone else this early in pregnancy?

How do I prevent it from possibly happening again?

note: not sure of bp or iron levels as I see my midwife for our first apt next week, but I do eat often and eat a decent amt of iron containing foods.

my pre natal is calcium /iron free