You are yourself saying it's a mystery, so why do you keep saying that the only solution pretty much is linked to anxiety ?
What makes you say that ? Research suggests that bad trips could make HPPD more likely to appear, but again, it's just speculation. Many people have HPPD without any anxiety or caused by a traumatic event.
This sentence applies to you as well. Your answers make it look like you are the one with the solution.
Mean-fucking-while, there are people who have looked into every single possible explanation, anxiety, neuronal, immune etc etc etc, dasitmane and others are no exception.
Trust me, we are open to all ideas, even the weirdest ones, but being so stubborn to say that the only way out of this mess is by focusing on anxiety and anxiety only is stupid imo.
Even actual research, people who know what they are talking about, found no proof of anxiety triggering HPPD. It can worsen it, but not cause it.