Thank SO much msdD, you are fantastic!
Yeah, I've read a bit and it does sound like prediabetic small fiber PN. So I've modifying my diet and been monitoring my glycemia and will soon be having data from the standard glucose load test and insulin so HOMA-IR, etc.
Once my sugar levels were better the burning seemed to subside, but the morning after the day I misbehaved and had some sugary drink that I shouldn´t have had, it was back again.
So this "acute" effect is what puzzles me: it is real or I just a coincidence?

Anyway, thanks again for the pointers to fructose, that stuff is now in everything, pure poison

I hope you're doing well yourself.