Benzos are usually seizure preventing and shouldn't provoke one, also the combo might have knocked you straight out depending on alc levels and tolerance but of course everyone is different and interactions are so too.. the prolonged DT might have had to do with the seizure(s) though, and both combined with the impaired memory..
Was this your first seizure or did you have had before?
Sorry to hear what you've gone through, had a somewhat similar experience when I did lots of dextromethorphan and drank lots in the evenings to relax and sleep. One day I woke up in psych ward, very confused and total retrograde amnesia- I had been there for 7 days already, multiple seizures when I never have had one before. I think chances are that wrong medicine contributed to the overall worsening as reason for admitting to the ward was just alcohol and me arguing with police..
Would be interesting if you recognize the pill, but still there are plenty of fakes especially about benzos (and opioids - of course these which are searched for) and they can contain anything. From your description of the jelly body sensation I had to think of the antipsychotic clozapine because it felt exactly like this and lowers seizure threshold.