Some people are clearly more sensitive to synthetic cannabinoids than others, and I'm unfortunately in that first group, together with the original poster of this thread
A few monts ago I took two or three hits of pure JWH-018 from a smoking pipe (didn't measure it, just eyeballed a tiny pinch, which was obviously a very big mistake!), and noticed the effects immediately. At first I felt motion sickness and had difficulty standing upright. I felt as if I was inside a spinning wheel moving way too fast. Then I started to gradually lose control of my body until I couldn't move any part of it voluntarily. I couldn't even open my eyelids and had to remain "blind" for the rest of the trip, against my will.
The first minutes were nice and enjoyable, but when I lost control of my own body things started to get ugly. I fell on my side and crumpled into a fetal position, and shivered violently. Then I vomited, and kept shivering for almost two hours. In the meantime, my heart was beating rapidly and I felt a VERY VERY strong burning sensation in my heart, it really hurt a lot, and it scared the shit out of me, because I thought I was having a heart-attack.
Thankfully, the effects finally waned after approximately two and a half hours. And I slowly recovered control of my body and my pulse went back to normal.
My friends were about to call an ambulance just as I was recovering. If I had remained in that "catatonic" state for a few more minutes, I would probably have ended up in the hospital
