Panic attacks are pretty nasty and as a former sufferer myself I can tell you that lifestyle changes such as exercise, a balanced diet, and stress management will work wonders. Also I reccomend Fish Oil as it contains Omega-3 and that combined with general good nutrition can work wonders. In terms of Cannabis it is really pretty dependant on the strain. I would reccomend Indica as that seems to relax me and make me less prone to anxiety of any type. If all else fails you could see your physician and see what he has to say.