My heart rate increases out the blue with shortness of breathe then I become faint and I feel like I'm doomed, ive had this happen to me 5 times in the last 2 years. It lasts from 10-20 min then body shivers for a hour or so, I experience inches all over then I return to normal. I went to the ER the last time and all tests came back normal, my blood pressure was high but it returned normal around the same time the shivers stopped. The doctor couldn't give me a reason that this happened, what could've caused this?