Did 20x with a couple pals a few years ago.
As soon as I breathed out (like, literally while the smoke was still coming out of my mouth) I started laughing uncontrollably at a very high pitch. I stood there laughing while my friends stared at me confused for what felt like 10-15 seconds, then got kind of dizzy/light-headed and fell back into my chair.
The chair in question was a recliner, so I sank into a lying down position and kind of curled my legs in. After that, I had essentially no control over my body, I could sort of slide my arms and legs along the chair but couldn't lift them.
Visuals quickly crept up on me, I'm honestly not even sure if I had my eyes open or closed. Body felt very tingly, there was a sort of vibrating feeling in the space between my lower ribs and my pelvis that was extremely uncomfortable, felt like I had a vibrator inside me or something.
The next part is kind of hard to explain. I've said a few times that I felt like I was a train, but that's not entirely accurate. What definitely happened is that the arms of the chair seemed to become like a tube, and the table we were all sitting around was the end of the tube. Since I couldn't really move, I felt trapped inside it. Somehow I got it in my head that I was waiting for something to happen so that I could move again, and that kind of transformed everything to feel like I was a train waiting for one of those railway turntables to swing me over to a new track so I could move again.
After that, I pretty much just waited. The experience was uncomfortable, what with the vibrating and my being pressed up against a cold metal chair, but not much in the way of crazy stuff happening. It felt like a long time just lying there, but it was only five or ten minutes.
Eventually, the feeling of being unable to move faded. I think I actually lay down a lot longer than I needed to, but I just got in my own head and thought I couldn't get back up. By then, I was back in the real world, but pretty high, similar to as I'd been smoking weed. That high only lasted a little while, though, and then I was normal.
One of my friends claimed to have a much crazier trip, but I think he just makes this shit up.