I wish I could answer your question, but honestly the same thing happens to me. It's scary because then I wonder if what I have is actually anxiety. I think that it's just that our minds are so conditioned to thinking a certain way, even when we try to think positively it can backfire. The most important thing is to just keep telling yourself that you are fine and you're going to be fine. This whole process of dealing with anxiety can be two steps forward and two steps back. Hang in there.