Perhaps your panic attacks have been caused because the potency, the amount of THC in marijuana, has increased. High amounts of THC have been documented to cause panic attacks. Over the years the percentage of THC in Dutch marijuana went up from 2-5% to well over 15-20%. I guess the same has happened in the USA. The government in the Netherlands is trying to pass a bill now to ban all hash and marijuana sales with more than 15% THC.
So just like Scolova said, perhaps you can try to smoke small amounts or try less potent marijuana.
PS. Sooners, taking a Xanax before smoking marijuana would help, but remember that Xanax is addictive in the long term too.