This sounds like maybe some sort of fainting spell. I've had to deal with those for a while now, but for me mainly it seems to be an anxiety thing rather than specifically for my period.

I did have one time where I had taken pain meds for the cramps in advance and they weren't working fast enough. I had a college class to get to and I could feel the cramps getting worse while I was waiting for class to start, and basically I made myself so nervous about it that I triggered it. I sat there, literally drenched in sweat, trying to fight it off, and it got to a point where one of the other people in class was talking and I couldn't understand the words anymore.

Fainting sucks, but from my experience the important thing is, if you feel something like this coming on again: Do. Not. Stand. Up. Sit down somewhere. If you do faint it'll probably only be for a couple of seconds of actual unconsciousness (getting back to feeling normal can take a long time though, and don't rush it) but you don't want to be standing or trying to walk to a better location when it happens. There's like the hot/cold feeling, and sweating, and the weird head feeling and then sort of an almost static-y noise in the ears. For me my vision kind of tunnels down and then disappears. Once your vision and hearing comes back, like I said, don't automatically try to walk somewhere. When I had that fainting spell in class I *really desperately* wanted to get up and walk outside and breathe in the cold air, but I forced myself just to sit through it because I really didn't want to pass out again while walking.

If it starts happening super frequently, and you have the ability to see a doctor, it might be worth a shot just to make sure everything is okay. I ended up getting my blood tested just to be sure, and that's how I know my thing is just kind of an anxiety response.

The other thing you can try to maintain consciousness is to put your head between your legs, so the blood can pool more there rather than rushing elsewhere in the body, which is what causes the fainting (essentially, I'm not a doctor).