Oof, that doesn't sound good.... Not fun at the very least. Yeah, the baseline of shaking sounds like what I was describing. The other stuff, well I'm not educated enough to really say what it does sound like exactly, but it doesn't sound like anything I've ever at least personally experienced with these tryptamines. I mean, I've twisted into all kinds of bizarre shapes on tryptamines, but not uncontrollably like that.... I'd say taking that benzo was probably the right idea at least for now.
I suppose you can elaborate on the gaps in your medication.... That probably would be a wise idea when experimenting with these chemicals though as long as it doesn't cause any problems for you in its own right. It's good that you haven't had any negative interactions with bupropion and tryptamines before, but that certainly doesn't mean it will remain safe forever or with all tryptamines, and based on what bits of information I do know about seizures, I would also be afraid that you might become more sensitive to it over time if you let yourself get into that state repeatedly.... It's hard to say how the gabapentin would interact with it too, the intuitive thought might be it would block it through anticonvulsant effects, but it's ultimately really hard to say how all those different mechanisms combined will turn out in the end, and it's not unheard of for drugs like these kinds to do the exact opposite of what they're generally supposed to.... That's why I personally like to just limit the interactions as much as possible when doing these kinds of explorations, at least until I understand how something works in my body pretty well first.
I really do think this one feels special too, and I hope you're able to get something out of it without having to deal with that heavy body load in the future.... I'll certainly be interested in hearing what you think about when you give it a try.

I'll keep an eye out for this trip report too, I'd be very interested to hear how this one went in more detail if you do get around to writing it.