What causes dissociation in a physiological sense?...........Well, in terms of HPPD, it's caused by changes in the chemicals and events that occur in the synapses but a lot of things are at play when you talk about dissociation. For example, if you were to take a large dose of PCP, you would also be feeling the anesthetizing effects of the drug as well as its hallucinogenic properties. If you have enough symptoms/side effects from these sorts of drugs, you will feel disoriented, panic, tunnel vision, can't catch your breath, and out-of-body feelings etc.
It could be density of serotonin receptors, neurochemical depletion, changes in norepinepherine and dopamine, etc. I'm not totally sure, i'm not a neuro-chemist or a psychopharmacologist. lol I think if someone was 100% percent sure of the cumulative effects, as well as the immediate circumstantial effects, of every cigarette, joint, poison, virus, bacterium, hallucinogen, dissociative, opiate, allergen, antibiotic, etc, that you have every taken or accidentally caught or ingested, you would still have a hard time finding an objective answer as to why you are feeling dissociation and a hard time finding what is going on at the biological and neuro-chemical level, given the subjective nature of any individual (certainly considering the possibility of genetic and premorbid disorders that may be latent).
That being said, while i don't know for myself, if the doctors knew for sure, they would have cures perhaps for HPPD.
There are obviously shared anatomy between all (most) humans, and shared feelings, experiences, as well as shared neurobiological and neuro-chemical actions.
Though, people have different sensitivities.
It all has to do with where psychology meets biology: where mind and body meet: the central nervous system. What is consciousness and perception?
The problem is, is that you are having problems with the definition of your perception. Reality is skewed and distorted and there seems to be some fog between you and the stars and you can't make it out. And you aren't feeling good. The biggest problem is that you aren't feeling good. And you are confused. I feel this stuff too. It should start going away at some point.
Dissociation is something that needs time and professional guidance.