I regret not taking psychedelics, but I hallucinated from a large dosage of hashish and had visual disturbances for a couple of days after, so I figured it's better to not mess with other psychedelics.
I also got a bad panic attack from a moderate dosage of stimulants(bad idea mixing them) and I could not drink coffee for 2 years, or I would get a panic attack just from the coffee -- it all went away eventually and I can drink coffee without a panick attack now (though it does seem to cause joint pain so I try to avoid it).