Guys what you name "long term comedown" I name it "Depersonalization/Derealization".
I got it at first somewhere in 2007 year, due to a wrecked mix beetween marijuana bad trip and salvia. Took me 4 or 5 month to recover. Since Im an idiot I continued to get high, tested more salvia in 2009 and ended with another 4 month DP/DR. In 2010 I got 2 or 3 month DP/DR from marijuana binge.
Then now, I took too much 3MMC and Methoxetamine in 2 month, and gone freak for 1 week and Im actually in 3rd week of DP/DR from a 3MMC binge wich ended wrongly.
Symptom are fare less severe than the first week and seem to improve, my mental ability/wit/clarity/reactivity is back to 100% (or at least cant tell the difference), there is just lingering perceptual/emotionnal problem wich I really hope will pass in the next 3 month course. Im still a bit scared even if used to the shit.
Methoxetamine don't seem to affect the state (I binged epic dose for 3 consecutive days with no effect on the problem).
These episode are IMO not really brain damage (at least not categorical, big brain damage like XTC litterature suggest), it's probably just a thing that some individual can experience without having that much damaged their brain, from all kind of substance. The website dpselfhelp is full of story like that, you will be amazed by the fact that even caffeine was at the origine of DP/DR in some individuals.
If you took 1 time XTC then got DP/DR, chance is you are far far far less damaged neurologically speaking than a 5 year weekly abuser. It's probably just a mini trick on your brain, perhaps even not a damage.
Just a neuronal pathway playing trick with you and don't wanting to shutdown, perhaps

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Brain Fog, short-term memory loss, trouble focusing, NO motivation... and other weird stuffs. I can't quite explain it perfectly, but i've felt very off for the past 4 months, like I've been in a dream.
classic DP/DR symptom
Erectile dynsfunction, especially if it present in the form of sexual anhedonia or stuff like that should be looked at with attention, thought... DP/DR don't include this symptom. I agree here it sound more like an insult to the serotonergic system.
Sry for my english Im french