So, I sort of get these from time to time, but I notice that it hits the worst when :

1. I've eaten like crap. Things too heavy I'm grease, processed food, and red meats. When I'm rating cleaner, I don't feel as panicky

2. If I feel the panic coming on, I HAVE to do some sort of aerobic exercise in that first 15 minute "induction" phase of smoking. Otherwise I'll carry the panic along through the entire session.

FWIW, YMMV