Yes, I get heart palpitations too when I don't take electrolytes. You need a certain ratio of sodium, potassium and magnesium. I also recommend drinking at least 200 ml vegetable juice per day. That doesn't kick you out of ketosis or autophagy.

In all medical supervised fasting clinics they don't allow a pure water fasting. A small dose of carb is highly recommended for absorbing and buffering the electrolytes.