So I was sitting in my couch watching a movie when suddenly I felt a heat wave all through my body and as well as a body rush. My heart started pounding fast so of course I thought I was getting a heart attack. But then I started getting a panic attack to I started doing breathing exercises. It slowly started going away then I started getting the shivers like if I was scared or nervous. Now I'm calm. I haven't gotten one for almost two weeks now but suddenly I get one out of no where? Do these come out of no where??