This is the only really bad trip I've had on shrooms and it happened the last time I did them. I've done shrooms at least 30 times and only had minor "bad parts" of trips where I cried or felt scared twice.
The last time I went on them there was four of us, myself, my brother and our girlfriends(I was visiting my brother who lives six hours from me). I suggested we go on shrooms and my brother got some (although he paid more than I was used to). We all took about a gram and a half of very dry cubensis (with food) and started watching Half Baked at 8:30pm.
After about an hour, my brother and my girlfriend said they were really feeling them...meanwhile his girlfriend and I weren't feeling a thing. They looked like they were really tripping out so we were makin fun of them but they were out of it. They could only spit out that they were really fucked up and not in a good way.
At 1:00am we still hadn't felt a thing and they were coming down...we all went to bed but I smoked a joint first. As soon as I put it out, the walls started melting and everything looked like a kaleidoscope or gas spilled in water. I could feel my blood rushing to my head and my heart pounding. Soon it didn't matter whether or not my eyes were open because it looked the same either way. At one point I could see heat like the Predator. With my eyes shut I could see the white aura of the candle on the desk and my girlfriend's glowing body on the bed.
She saw how bad I was tripping and told me to come to bed. I was oblivious to this for quite a while and finally she dragged me to the bed. I started to beleive that this trip was so intense that my mind would be fried when it was over. I kept saying that I was "going to wake up retarded" and then I felt more like I was going to die. My heart was beating violently and erratically and I thought it would soon give up. I cried and shook and spasmed for about an hour until I guess I passed out.
The next day we all felt like shit except for my brother's girlfriend who had never felt a thing.