Alex, I think that you and I have a lot in common. My first panic attack happened while I was out for a run Christmas Eve morning in Ruidoso, New Mexico. We were vacationing there. What should have been the most beautiful run of my life -- snow on a dirt road, deer out and about, mountains in the distance -- turned into one of the worst experiences of my life. I felt like I was going to pass out on a secluded street in a strange town. Several times, I walked until the dizziness went down, then resumed running until I finally thought that I was going to hit the ground. I walked back to the condo and said nothing because I did not want to worry my family.
Like you, I've had all sorts of tests which revealed that I am relatively healthy. Also, like you, I have found it hard to jump back into exercising. Lately, I have done some walking and riding a stationary bike. It helps with my mood. However, I just can't shake this damn lightheadedness. Today, I was convinced that something physical was wrong with me. I was in a business meeting, and I felt like I was going to faint. While this was going on, I formulated a plan to go to more doctors to find out what was wrong. Well, when the meting was over, my lightheadedness went away 90%. So, obviously, it wasn't a physical issue.
At this point, I almost want to pass out just to get it over with. All I can do is challenge the thought, and go on with my day despite the anxiety. I wanted nothing more than to run out of that meeting, get in my car, and go home. I stuck it out though and am glad that I did because I don't want to fall back into a pattern of agoraphobia.
Best of luck to you.