Your brain. It's wild, and it doesn't function the same as other people's brains. It doesn't always even function the same in exactly the same circumstances. Now add a substance that makes it fire off even more randomly with hallucinations and watch it try to cope. Brains are so complicated that we haven't even figured out how they work normally without any drugs altering their function. Figure that one out, and maybe one day we'll figure out the bad trip.