I felt a bit jittery the first day. It wasn't debilitating, but it was noticeable. It was only a day for me, but I've read of kids craving bread for days. I was getting some acupuncture appointments during the same time period, and I'd just started a high-dose multivit/multimineral supp within the previous month (lots of caveats, I know) but I got a boost of energy 1.5 days after cutting out gluten and dairy. But during the same time period, especially when I emotionally accepted that I has a problem that was going to take a while to fix, I had a few weeks of even more fatigue, and fatigue was a pre-existing problem I was trying to address. I think it was the removal of the emotional stress--could it happen with the removal of a physical stress? Seems possible.
Make sure you're getting enough food. For me, fat and meat were really helpful, but I'm sure that varies somewhat.