I have had so many good, fun trips, mostly acid as a teenager, but I have had a few bad trips and had several friends have them too, they suck, but at the same time, they are part of the experience and can be turned back into enjoyment with the right consciousness.
My first bad trip was in the woods, in February, pony keg, 4 of us, all good friends, deserted campground, huge campfire in our favorite campsite. 1 guy starts to have a bad trip and crawls in his truck because he perceives an action by another friend as negative and doesn't know how to handle it. He doesn't come out until the next morning.
I get up to piss in the bushes, and it hits me, the wall of static 100 feet high in front and on both sides of me. Like TV static, the buzzing gets louder as my whiz hits the bushes in front of me. By the time I finish peeing, I'm frying, balls out experiencing one of the most sensory-heightened trips I would ever experience. I walk back to the fire, sit... I'm gone. My 2 remaining friends each fill up a pitcher from the keg and head off towards the trail. I see them fucking with the flashlights and then finally laughing hysterically, throw them to the ground and walk off into the canyon, it's about 10:00pm.
All of a sudden, to my right, I see the headlights of a car coming straight at me... this was the moment everything went wrong. I didn't know there was a road there. In all the time all of my friends and I camped there, we never saw this road or saw a car travel on it. I froze as the car turned and slowly disappeared down the road on the other side of the ravine. Over what I think was the next several hours, I went from wondering "did the people in the car saw me sitting there, in February, looking lost and call the cops?", to the panic of "Oh My God, am I sitting in the rubber room with my family staring through the glass at me, and I don't know it?".... Bad, bad trip.
I came out of it when my 2 friends returned from their hike about 2 or 3 am to get more beer. They had a blast, my friend in the back of his truck had the worst time of his life and I, had a very bad trip, but not the worst time of my life. It was an amazing experience that I appreciate having, if nothing more than to appreciate the contrast of a good trip. If you fry, you may eventually experience one.
The second time I didn't know most of the people I was frying with and so as we sat on the couch watching faces of death, a cop walks in the door, puts his gun on the kitchen table, walks in the room and sits down on the chair next to me and proceeds to join the conversation... *&%$!@#??!?!?! It was one of the guys roommate... he didn't tell any of us first. The night continued downward from there until I finally found the corner of a hotel room of someone I didn't know to sleep in. I woke up the next morning, walked out of the room and called a friend for a ride.
Keep all thoughts positive, don't fry with people you don't know, establish your environment before hand and stay there! LOL...