Again, just because there is a psychological component to this disorder doesn't delegitimize it at all. Whether or not you have control over something like this has nothing to do with whether its physiological or psychological. Few people can control the brief moment of fear & sphincter clenching when they see a police car in their rear view mirror and that's entirely psychological, almost everyone can control their breathing or eye focus to a certain extent, which are both physiological. At any rate I'm certainly not saying its entirely psychological. I just think, and there is pretty good evidence for, that HPPD, much like PTSD, starts as a psychological phenomenon which, when it occurs often enough, leads to changes in neuroendocrinology & neuroanatomy, just like any form of learning.
Take PTSD for example, and forgive my brevity. It starts with a strong psychological imprint, in this case fear. This can cause NE/cortisol levels to get out of balance and negative feedback inhibition of cortisol can cause (or may be caused by, who knows?) irregularities in the Hypothalmic Pituitary Adrenal axis, then by proxy the hippocampus and amydgala. The latter is involved with highly emotional memories. Once all these things have occurred, any number of stimuli associated with those painful memories can trigger an acute incident. So what you basically end up with is a dysfunctional learning pathway associating feelings of dissociation & fear with any number of stimuli that are or have come to be associated with the initial trauma.
I don't think its that much of a logical leap to assume a similar malfunction can occur with any type of intense psychological imprint, like one from an intense (positive or negative) psychedelic experience. Obviously the visual component is more pronounced in HPPD, but many PTSD sufferers also have hallucinations or visual irregularities. All this being said, when one starts to enter an altered state through something like d-amph, pot, or both, these feelings of "alteredness" can trigger the dysfunctional learning pathway that has formed as a result of the initial psychological imprint.
And lastly, I could be wrong on this, but floaters, if what you're refering to is the same thing i'm thinking of, are just bits of more gelatenous vitrious floating across the retina and casting a shadow... shouldn't be a result of drug use. I think everyone has those