Just finished the fast this weekend. It was more to challenge myself mentally than physically. Basically what I did was a 24 hour fast, broke it with one keto friendly meal (with LOTS of protein), followed by an additional (almost) 36 hour fast. I say almost because I broke it 35 hours in, felt it was enough.
I will say from this experience that I was EXTREMELY low energy, but not in recon at all. In fact, I felt mentally at peace much of the time, just physically exhausted from the lack of nutrition.