Spill the beans? If you aren't in a familiar setting, with people you don't know, are afraid, had a bad day, have something weighing on your mind, are paranoid, then you could easily have a bad time. It probably won't mess you up emotionally/mentally permanently, but it can indeed change the way you think and view the world. At the same time, a really good experience such as I had, can change your whole perspective and interpretation of some things. Also, a really bad trip can teach you valuable life lessons, so in reality, it was actually a good trip. Does this make any sense? It's also to talk yourself out of a bad trip and reason it into a good one at best, or ride it out at worst.
With some things, it's not getting high. It's just so much more meaningful that that, and the word "high" just seems to cheapen it somehow. It's just... I dunno. You just can't describe some things. It's like trying to tell a world of blind people about a rainbow you felt.
Ant, watch this video and follow the instructions. That's a decent example of what happens when my HPPD manifests it's self. Actually my HPPD isn't nearly as strong as that video lol. When i'm reading, text will float as if it's on a ripple in water, enlarge a bit, move back and forth. Pulsate is a good word. Walls, floors, etc. will breath and pulsate. It's not nearly as strong as the video, but you can get the idea of what a very (very) basic hallucination looks like.
http://youtube.com/watch?v=vzSRVgF501M&feature=related
It actually started after my first time and never went away. Don't get me wrong, it's entertaining and maybe happens once a week now.