Like something is gripping your heart. Your chest feels tight, sometimes to the point of a sharp pain. Can't control your breathing. Hyperventilating or not breathing at all, or at least the sensation that you can't breathe. Heavy, rapid heart rate. Sweating. Cold fingers/hands. It's like opening a shaken up bottle of soda, and it's uncontrollably spilling everywhere, and you can't get the cap back on, and even if you do there's already such a mess to clean up. And then instead of helping you clean up the mess, people ask why you made the mess and tell you how easy it is to open bottles without having them spill.