I saw something about target panic on TV just a few nights ago. I don't remember what the program was, but the guy said that it is usually due to too much practice, if you can practice too much.
His advice was to back off and only practice about 2 times a week until the target panic goes away. He basically said that it comes from practicing so much that you start trying not to miss instead of trying to hit the target, if that makes sense.
I think it came down to a concentration issue. Some have suggested concentrating more, but I got from the guy that too much concentration about not missing was the problem. I suppose like all things, it will vary from person to person.