"What could happen if you are too physically active during a fast, is electrolyte depletion, which can cause an irregular heartbeat. However, this only happens after a longer period of fasting. And personally I believe that it's only possible if you fast on distilled water, as this draws too much substances from the body."
you dont need to be fasting long for this to happen. you might be starting the fast unbalanced. its a danger on any type of Water Fast especially because you are not putting in what you are sweating out. essential salts that deliver the body's signals to the heart to beat. this is what i have researched. the end result beyond irregular heatbeat is heart failure.