Add one more person who’s experiencing the same symptoms. I found this thread out of desperation in trying to understand if this was normal or not, as I was ready to find a doctor to check me out. The pain came on quite suddenly right at the very beginning of day 4. It was absolutely excruciating and was almost impossible to sit, lay, drive or sleep. Had to prop several pillows all around me to find a pain level that would allow me to fall asleep, and then had to shift my body position constantly. Almost no sleep for 2 days.
For context this was my first fast beyond daily fasting. I consumed only black coffee, green tea, water, and herbal tea during the fast. I had approximately the same amount of coffee as I normally do, 2 cups.
I did add Trace mineral drops to my water as well as Celtic Sea salt, plus some additional magnesium each day. Day one was easy, day two I was very lethargic, day 3 I actually felt okay. Never any hunger pangs. I had a suspicion of potassium deficiency because my trace minerals didn’t have a lot of potassium in them so I added that the day after my pain started. As everyone has described the pain seemed to start in my lower to mid back and radiated downward through the backs of my thighs down to my knees. My primary suspect was the kidneys, perhaps due to the large volume of liquids I was consuming each day. I broke my fast shortly after the pain started as I was afraid it could be a serious problem. The pain level went from a 10 on intensity down to about a 7 after eating and adding potassium. It then slowly dwindled down from there but it would come and go at random. Laying down was the worst, but sitting down was a close second. Going for a walk seemed to help alleviate a little. It mostly subsided after about 3 days of breaking the fast.
I was hoping to find the answer in this long thread but it looks like this is still a mystery to everyone. I thought about the caffeine theory, but I had the same caffeine as usual and I can normally go weeks without any caffeine with no symptoms at all. So I’m reluctant to say that was the cause for me at least. I could see it affecting someone who is more sensitive to caffeine though. The uric acid explanation is interesting and has me thinking. I’ve never had gout so I’m not sure if that was my problem. I would be willing to try the ACV mixture as described though to see if it had any effect. I probably won’t do another fast anytime soon due to the serious impact the pain had on my work schedule, but I will check back here for additional updates hoping that somebody is able to identify the root cause. Thank you to all in this thread for your input and helping me to feel at least somewhat normal.