I felt exactly like that once and only once and oddly enough it was from the first time I ever smoked. Then again, with my friends, if it's your first time smoking they will pack bowls till everybody in the room is out of weed, I think I had 13 bowls in a two hour period. But I know exactly how you felt, I kept asking everybody how long it was going to last and felt really anxious like the feeling was never going to go away.

If you don't smoke that often or if this was one of your first times you should build up your tollerance a little more so it won't be that bad every time you smoke. If you do smoke regularly then that must have been some great bud!!