Same thing that gets everyone on a fast, too much water, not enough electrolytes.

Essentially got really really bad cramps in my legs each morning towards the end of the first 30 days. Fixed itself as soon as I added in the magnesium and potassium supplements. Likely caused because I drank too much water during the early parts of the fast.

Interesting! So salt, Magnesium, and potassium only. I want to try fasting for a week or so. Is there a specific type of these supplements you recommend?