ah, the old "fasting to completion". That's what I'd intended with my first water fast. I broke it on day 29 with some watermelon, that tasted like cardboard. That should have been a sign to me. The upshot of it all was that it took me about three weeks to start feeling normal. To get strength back and also a feeling of real appetite. You might be wondering, why would I quit when I did. I had entered a sort of mini-"crisis"
of spitting (salty saliva). This started in week three (edit: make that four) and I just got very tired of the experience. Knowing what I know now, I would have carried on.
My second longish water fast was 21 days. I stopped then because I felt "up", proving to me that this is critical. I had a bit of eye congestion for a few days--again, probably should have gone longer, as the eyes were being worked on, but I weighed all the factors, and didn't feel I could do the possibly two more weeks it might take...
With longer fast II I felt good almost right away.
Also have done a number of shorter water fasts, of 3, 6, 9, 11 or so days. These were all good, and pretty easy. There is one school of thought that says shorter fasts, of say, a week, might be as beneficial as the longer ones. I like the extreme internal quality of a longer water fast, and I have a little weight to play with. I'm about twenty pounds or so, away from ideal.
I feel strongly (as do some of the 'fasting masters') that the WFast works in seven day cycles. (also, of course in longer 28 day cycles. I think I started a new cycle, right as I broke the fast on day 29, and this made it a much harder post-fast. No vomiting or anything. Just slower to be able to feel 'vital'.)I also believe (this is my own guidance speaking) that for men, the cycle can most often be 21 days, while for women it's most often 28 days. (There are exceptions) These cycles apply to water fasting especially.
I would encourage you to pay close attention to your own experience, and since we are more water than anything, and water is intuition, (and intuition is sharpened by 'nothing but water')to heed your intuition. You might find that 21 days feels right. Or, you might feel like going on longer. Basically though, it doesn't make sense to break a fast if you are not feeling hunger.
It's more likely though, these days that we run out of reserves, and end up feeling either extreme boredom, or an extreme weakness; in the latter case, sipping tiny amounts of juice, diluted, might be just the thing. Some go for the mineral-rich broths too.
From what I've read, the more common experience is that the fast is broken before a return of "natural hunger". With the shorter ones, some people complain they feel hunger all the way through, but this (I believe) is more mental. With the second water fast I actually began to feel genuine hunger, I think! enough that my first sips of juice were heavenly. But also, I has mentally attuned myself to not wanting to repeat the previous 'crisis'.
best C