I guess I've kinda freaked out once.
the first time i smoked a waterwall i kinda got really zoned out, I started having a lot of trouble controlling my breathing, i would just forget to breath until i was on the verge of passing out from not breathing and than start breathing extremely hard. and no matter how hard i tried i just couldnt remember to keep breathing frequently. i started feeling really sick and almost threw up. i just had to lie down for a while
i noticed later that i'd burned a lot of plastic into my hits on accident, but i dunno if that would make that big a difference or not.