Holy FUCK! How does THAT happen?!
If you're the dude getting KO'd there, how do you come back from that? How do you show face in the gym the next week? You couldn't defend a head kick from the canvas?! You let it FACEPLANT you?!
Listen, I'm not saying I could defend against this, because I'd never see it coming in a billion years (and would likely never be in an advantageous position over an opponent in a fight) but I also don't think there's any coming back from this if you're the guy who let it happen.
You get KO'd by a grounded head kick - MMA probably ain't for you.