So, for the past few days there's an extreme heat where I live, and this morning I wake up earlier with my heart racing and pounding to the point I can hear it in head, shortness of breath, sweating (it's hot weather, so not sure whether panic caused me sweat more), pressure/squeezing feeling in chest with stabbing pain... All this goes down while I'm sitting on bedside after waking up, maybe after 2 minutes heart rate reduced (no more pounding sound in head), still felt some weird chest pain, but I lied down, took metoprolol (since it also dilates blood vessels) and continued to sleep 4 hours, woke up and for almost 18 hours I haven't felt any such chest pain. Though my blood pressure is lower today which makes me think, what if I have a heart damage?... 

Been to ER like 7 times in the past year, always sent me back home with normal blood test and normal EKG. But I can't have my mind at ease now unless I've done EKG and troponin and CK-MB test, I am anxious as hell for many days following such events (I guess this is cardiophobia or something).

Not sure what to think of this, could this be heart-related, a panic attack, adrenaline surge, coronary vasospasm due to anxiety/panic? Has ever experienced something like this?