This is what all my difficulties have ever sprung from. I've never had like a "I'm not ever going to be sane again!" or "What are those crazy monsters?!" type thing happen. It's always just this thought that I can't escape from. It might not even a bad thought, it's just confusing to always come back to that same though no matter what else you try and think of.
Most of my friends and I don't really get bad trips but it does happen from time to time. I remember one of my friends was caught in this thought loop of "what do I do?" That's all he could think. We would try and reason with him asking "You mean like right now, or something with your life?" and he was just so confused. You could tell he would try and process it but he would just come back to that thought of "What do I DO?!".