I was googling this very topic when I came upon this thread, with a bunch of great responses. I hope I'm not reviving a dead thread here, but I'd like to reflect upon my experience to.
I had been a heavy pot smoker from about 2000-2006. I mean real heavy, as in...pick up an ounce and it was gone in a few days to a week. Anyways, I had been experimenting with some other drugs at the time (extacy, shrooms, coke) I had started having my panic attacks. I can trace it all back to one event. In the summer of '06 I went to a party with my girlfriend at the time, and did a particularily large batch of shrooms in a depressing 80's style basement apartment, and had a terrible trip for about 8 hours.
I had smoked weed for about a month after that until I started having panic attacks, which I know where linked the that event. So I tried cutting back, and I kept getting attacks... I'd get anxiety, my throat would swell up, I'd sweat, my mouth would be drier than usual, my breathing would be faint.
It's been approx. 3 years since then, and I still can't smoke weed, because of the same problem. I've pretty much quit (I smoke once, on New Years, thats it.).
It's a very good probability that what the others and myself here have experience is what you're going through. Unfortunately, I dont think any of us have found a comfortable way to continue smoking, and we've just given up.
It's really a shame, because I wouldn't mind smoking again, it's just that its not fun like it used to be.