Thanks for the description. I haven't had a full-on carb out for several months.... unless you count the pudding I had at the end of October. At that point I had been fully keto and sugar-free for about 6 weeks, after another couple of months before when I was mostly keto.
So I ate this pudding... and within 1/2 an hour It felt like my bowels were going to explode, I felt flushed, and my BG an hour later was 8.4 (when I hadn't seen more than 7 for several weeks)
It certainly puts me off indulging again.... and your fish and chip story does as well.