Same here. That happend once in my friends basement. After we all got done matching bowls out of the tube, I was getting ready to spark a cig, and my heart just started pumping so hard. This lasted for like 5 mins. I went outside, took some deep breaths, and I was fine. I think I had a panic attack, because I was really high and i probably had to go home or something and I jsut started sketching out about it. Same idea as a bad mushroom trip---No fun