I freaked out like that once. It was the first time I got really blitzed. Exact same symptoms. Thing is, it's all in your head, my buddy took my pulse and to him it was normal, but in my head it was pounding out of my chest. You just have to calm yourself down, because as long as you know what you're smokin', you shouldn't have any worries. When I freaked out it was out of the same bag I had smoked from 10 times before. The only difference was that it was all dried up.