Cotcha, what are your thoughts on antipsychotics and remeron increasing HPPD? They seemed to have helped you, and you stated you had HPPD.
Mirtazapine is pretty unique, I would expect it to help HPPD a bit but that's my experience. Depends upon what dosage I suppose, higher doses where it becomes more adrenergic I would expect worsening of visual symptoms given that people report worsening of HPPD with anxiety. Mirtazapine helps me sleep and that helps my HPPD so that might be my uniqueness if other people are reporting worsening of HPPD with mirtazapine.
On the other hand Risperidone (anti-psychotic) helped my HPPD even though there are clinical case reports of Risperidone worsening LSD induced HPPD. This could just be me sleeping better though. Risperidone worked great for helping me shut off my thoughts, although at higher doses like are used to treat schizophrenia, it can cause dysphoria/anhedonia and movement issues. I personally never had any issues besides sedation, which of course I desired.
I remember now we were talking about loud noises startling the other day so I'll mention, anti-psychotics pretty reliably raise pre-pulse inhibition, a measure of acoustic startle reflex that is often talked about in sensory-gating/sensorimotor gating disorders and schizophrenia. HPPD is thought to also be an issue with sensory gating, and some of the genetics that overlap with sensory gating issues probably overlap with pre-disposition to developing HPPD, like the gene for the 5HT2A receptor, the principle receptor responsible for psychedelic's effects (and MDMA's major metabolite MDA is also active at 5HT2A). Risperidone is a major blocker of 5HT2A, mirtazapine is as well though you may not see significant 5HT2A blockade until you're at higher doses, and then other effects are confounding.
So personally Risperidone helped me a lot although its not a drug I would want to be on for decades. But I retained the benefits of having been on it. A lot of the benefits of being on anti-psychotics are probably genetic in origin (same with anti-depressants), and thus these aren't benefits that are going to just disappear when you taper off the drug, as opposed to what FBC has said about medications for schizophrenia and depression making the diseases worse in the long run, which I have to whole heartedly disagree with.. Very ignorant of him to say.. But your mileage may vary, everyone is a unique snowflake. 0.5mg - 1mg risperidone is also going to be astronomically different than 4mg risperidone. At the end of the day the doctor is the one to talk to. My two cents is that if insomnia is causing a lot of the issues and you want a longer term drug for insomnia (one that will leave lasting beneficial effects), Risperidone is probably the one I would choose. But it is an anti-psychotic and they're not to be taken lightly.
As always any questions are welcome. Also guys I'm sorry if this is getting too neurosciency and shit.
Edit: I managed to find this old study I thought you might be interested in related to acoustic startle after MDMA abuse
https://www.ncbi.nlm.nih.gov/pubmed/14970829 - "These results suggest that the functional consequences of chronic MDMA use may be explained by 5-HT receptor changes rather than by a chronic 5-HT deficiency condition."