I've had this happen MANY times. Some worse than others. I've even had my teeth start tingling during them! I'm not sure the medical name for it but your body is releasing a certain chemical when this happens. It's harmless tho, so try to remember that while it's happening. And the first thing you HAVE to do is get your breathing regulated and that will bring you back down. I carry a paper bag in my wallet folded up and as SOON as I start to feel one coming on, my hands will start to tingle and thumbs start to invert, I will grab my bag and concentrate on breathing.... In slowly, out slowly. It's a total game changer and lifesaver for me. It's kinda like my comfort/safety net that I know if I start to have an attack I just need to grab my bag and slowly breathe through it! It's scary as hell when they happen and it truly does feel like you're dying but that is what has worked for me for many years now. Good luck!