During the second week though, the body pain and fatigue gradually kicked back in. Each day I felt worse than the previous one. The brain fog started up again too. By day 14 (a Saturday, so no work) I felt so bad, I just sat on the sofa all day doing nothing, and on Sunday I had a major migraine, D, major stomach pain and nausea, swelling etc. I couldn't eat a thing and retreated to bed for the best part of 2 days. Then I had to do the bowel prep for the colonoscopy, so didn't eat again until late Tuesday.
Was back at work on Wednesday feeling much better, having fasted for 3 days, and then returning to the gluten free diet. The abdominal pain and headaches took about a week to subside. Skin itchiness and breakouts still haven't quite got there, but they are improving. Ditto bloating/swelling and what I think might be lymph pain. Fatigue and body aches are still a significant problem, so it might be a while longer before I fully bounce back.
So the symptoms of a gluten challenge can build up quite subtly, and equally take a while to get back under control again. It is not something to be undertaken lightly. I felt that I couldn't have swallowed another mouthful of gluteny food by the end of two weeks. And most doctors seem to say that a gluten challenge should normally be for up to 3 months. Torture!