This is an old forum, but for anyone reading it. I had pretty bad panic that lasted about 5 hours. I think what may have been actually happening is that I was having one right after another, due to the fear of another. I'm almost to the point i can't tell the difference between high anxiety and panic. My first one was problably only 20 minutes, but felt like an all day affair. Left me shaken, depressed, and physically drained, dizzy, you name it.