I've done IMF for something like 9 or 10 years now. Over the last few weeks, I've been traveling and so far out of my normal routine, that I haven't been able to fast. Today is the first day in a while and wow -- I forgot how much better my brain operates fasted.
I'm not sure if you would, but that's kinda what happens to me. First theres a hyperactive but too scattered phase. But, once habituated, it's just easier to get into a "flow" when fasted than otherwise.