Its what causes most panic attacks. You shoot a lot of adrenaline into your system but not for a real reason. It's a misfire, Your body gears for some emergency that's just not there. You got all this adrenaline with nothing to do. You're not fighting anyone, or are you running away. So, your heart races, I get a feeling like a caged animal, my head starts feeling just weird. almost like I'm falling. I feel like I should be doing something I just don't know what. Sometimes if it cold out I go outside, cold seems to help. I need to open a window, or just put my head in the sink and run cold water over my head. But in some cases nothing works, so been to the ER a few times, given something like Xanax or some other meds that calm you down. Now I have some for an emergency. Plus I learned to deep breath and mentally relax. if it's a night-time attack don't jump out of bed, I keep a chair next to my bed to slide into. There I can start the coming down system I use. Remember once jumping out of bed while not being fully awake, had sleep paralysis, legs where like rubber. Had no feeling, guess how that made my panic attack just worse.