It sounds tome like your body had been "detoxing" in a sense and you may have introduced some foods back too quickly.
I know for myself, a few years back, I was on a sort of detox diet - no refined sugar, no flour, very light on root veggies. When I introduced everything back in, it may me feel awful for a day or two, but then I was ok. I think my body was trying to fight it. I had been feeding it so well for a number of months, that it didn't want the bread and other such things I was eating. I had been testing my BGs so I know it wasn't a BG issue for me, but you'll never know for sure until you test.