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.
> The crazy thing is, if you can get to 7 days, anything past that is just mental and you can go as long as you have the body fat to sustain the fast,
It's not that easy. You have to properly substitute electrolytes - sodium, potassium and magnesium. And that is almost impossible without small doses of carbs.
My longest fasting was 42 days. I did 28 days three times before. I'm fasting more or less regularly (once per year) for about 25 years.
Don't do very long fasting without guidance of a doctor. Your heart needs properly balanced electrolytes.
EDIT: I've just seen your other comments here also underlining the need of electrolytes. I still leave my comment here for the other readers ...
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.