Has this happened to anyone else

Hello ladies, I'm 16 weeks pregnant and earlier today I was at work (retail) and I started sweating so bad and next thing I know my vision goes black and I almost fainted. It was pretty scary, everyone was asking if I was okay but I couldn't see anyone faces really. So they had me to go sit down and I drunk some water and I was fine after 10 mins. I've been feeling kind of dizzy off and on all day after that. I tried calling my Dr a few times but no one answered. So I'm just curious, has this happened to anyone else, is it normal?