Hello!
I sure know what you mean. Instead of a yo-yo dieter I call myself a yo-yo anxiety/panic sufferer. Feel really great for a number of years and then Wham! Back again, like it never left. For me, I know it happens when I stop doing what helped me heal before: Exercise, relaxation, changing my thoughts, talking with someone, reading a good book on the subject, getting plenty of rest, taking regular vacations, spiritual help, etc.
Like eating right has to be for life to keep the weight off, I think we as anx/pan sufferers have to keep doing what helps us for life too. Because these things help us not to get weak and vulnerable psychologically and emotionally and so not so easily succumb to the BEAST. We are stronger and can defeat it easier!
Peace to you!
Spinnaker