I feel for you, man. I had a very rough year dealing with panic, I have always been a tough guy, never been to the hospital or Dr. for anything, all of a sudden I think I am having a heart attack once a week, then daily.
I struggled for a year, afraid to work out, walk, jog, anything. Then I slowly started an exercise routine, and felt better than I had in 3 years. I tapered off of zoloft, had no need for xanax for almost 3 months. Then one night BAM, while walking on the treadmill, my fisrt PA in over 9 months. That was two weeks ago, I had daily anxiety and had to start zoloft again, to my disappointment. I have the hardest time at work too, my job involves alot of physical work and local travel.
The good thing is, I KNOW that I am capable of going long periods of time with no PA's or substantial anxiety, it is just a matter of getting back to that state. It could take weeks or months.
The sad thing about panic is that it hits out of the blue, for me it is when I am feeling good.
Keep the faith. I know that this site has helped me enormously, knowing that there are others like me.
Eric