> it can be not HPPD but underlying psychosis or schizophrenia that has been activated by the drug

This is crucial part - tons of folks are a mess inside, and either it will never manifest fully (but they won't be perfectly normal balanced happy human beings either, just some grey zone), or it will with some shock - be it car crash, heavy alcohol use, tough breakup, death in close family or psychedelics for example.

My first GF's father had permanent paranoid schizophrenia triggered just by episode of heavy drinking during mandatory military service. Fucked up for rest of his life, on heavy medications.

Its not as rare in the population as we would like to think, still carries a heavy stigma with it so folks don't talk about it unless they have to.