Help! When do I stop a fast?

I always read that ideally a Water Fast should be stopped when the tongue clears and true hunger resumes. As I understand this is when ketosis stops and the body begins to consume proteins much more heavily. I'm taking a nutrition course and we just covered fasting and I've learned that the average person has enough body fat to last many weeks, even months, before lean protein is consumed seriously. Somebody put two and two together here for me, please - is this practice advocating fasts of extraordinary length? I'm not doing this for weight loss, mind you, but I'm on day 6 of a Water Fast (of undetermined length) and am looking quite gaunt, enough so that people have begun commenting. I was planning to go until my tongue cleared, but will that happen? If so, will it presumably happen within the next week or two, since I don't visually have much body fat left to lose? Should I stop sooner, rather than later, even if it doesn't happen? Tweet