Perhaps you just need a better environment to smoke in... are you smoking alone or with friends? It all depends on the person but some people get a lot more paranoid when smoking alone than with some friends who can keep you centered. For others being alone in a comfortable environment can help.

Also this could be a sign of some other unacknowledged anxiety issues that perhaps marijuana is just heightening. Perhaps make sure your head's in a good place before you decide to light one up again.