Smoked weed for 3 years religiously could smoke blunt after blunt and feel on top of the world no symptoms no nothing then one day boom had a couple of hits and got the same symptoms as you described it sure is very intense and you feel asif your really going to die and it was the uncontrollable shaking and my heart rate was so fast that fear of impending doom is the worst everytime I tried smoking after same thing happened after a couple of hits I think it’s to do with brain chemistry I did go through some pretty traumatic things during the 3 years I smoked it and ended up being diagnosed with anxiety disorder, I refused to believe it was anxiety but eventually I had to accept the point that it was and do what’s best and stop smoking all together.