Yes dude, it's scary ass shit!

I know that feeling. If I get too hot Ill get tunnel vision then start to pass out quick. So I have to lay down and put my legs up fast

I would get dizzy, light headed, very very hot, even sweaty, and clammy, and would literally be able to feel myself about to faint.

What damiensmommy said is true, and it could also be due to iron levels, or dehydration. Make sure to drink, drink, drink! You're doing right by sitting down when you feel that way though! Also turning on the air for a minute, or going outside to cool off as you sit down and sip water can help as well! I had this real bad throughout my pregnancy with my daughter, and have a few times this time too. It's a scary feeling, i've also had this issue not even being pregnant, at times after having her! It's scary cause I've actually fainted and passed out a few times over it, and had to have an ambulance called last time I passed out, because people got scared. After all is said and done and you come out of it, rinse your face with cool water, it should make you feel way better, if it doesn't, then you need to go be seen at the ER, to make sure your body is regulated and okay!

Are Yu Seeing Little Light Speckles Cross Ya Eyes ?

I was the same. I would close my eyes and the whole room would spin. It happened to me once so bad I literally laid in bed with my eyes closed for 30 mins while it felt like everything was spinning. I hope you feel better. If you need to, go to the er. Better safe than sorry. If it is your blood pressure, chances are you'll be sent to L&D for monitoring.

Could have something to do with your blood pressure dipping. Make sure you are eating frequently and drink ice water to help.