i had a similar experience before. i smoked so much i didn't wanna even be high anymore. it felt like i was having a heart-attack and irrelgular heart beats. the fact that i "felt" this almost made me piss my pants in anxiety. i sincerely though i was going to DIE. all from smoking a few grams of my favorite green
in retrospect i'm pretty sure most of the physical sensations during that time were psycosimatic (or however it's spelled... all in the head) and since then have learned to supress.