Here is a good link that you might find helpful...
For me, it took two courses for me to really feel better, and in control of my anxiety. That is two courses, not sessions, so I would say that it was about 20 or so sessions.
I also felt like I actually started to improve most toward the end of my treatment. Recovery started slowly, then kind of snowballed and it all started to happen quickly.
Try to remember that healing is not a linear journey. You are going to have setbacks, but that doesn't mean that you have lost ground. It simply means that you need to pick up where you left off, and keep positive that a better day is coming.;)
You have noted improvement with the work that you are doing, so that is a great sign!
Keep up the good work.
"Courage is not the abscence of fear, it is feeling afraid and doing it anyway!"
"Worrying does not empty tomorrow of its troubles...it empties today of its strength."
Corrie Ten Boom
Panic Syndrome recovery due to CBT