Phinney and Volek cover this in "The Art and Science of Low carb Living"

A good video with them here -
http://futurepaleo.com/video-jumpstartmd-interview-with-stephen-phinney-and-jeff-volek-about-nutritional-ketosis/

Info on sodium begins at 32:56.

In general though,
From "The Art and Science of Low Carbohydrate Living"
Low carb diets are natriuretic - they make the kidneys dump sodium. Sodium deficiency can cause headache, dizziness and fatigue. With continued low carb intake and sodium restriction, at some point your kidneys start to excrete potassium in order to conserve sodium. Potassium deficiency can lead to muscle cramps, cardiac dysrythmia. it can also cause the body to lose muscle, even when there's plenty of protein in the diet.

On keto, we should consume 3-5 g sodium per day. Broth is the easiest solution.

For an extra bonus - add 2 tbsp of heavy cream to your broth and get a fat boost at the same time!

One of my favorite recipes on Keto is a modified version of this: http://cavemanketo.com/chicken-broccoli-soup/

I dunno what my girlfriend does to it, but it's freakin' amazing!

ANYWAY, about the electrolyte imbalance, yeah, that's a huge issue with going into ketosis, usually attributed to "keto flu". I tend to stick around 5000mg of sodium per day, and I use Morton's Lite Salt which is about half potassium. If I can feel my muscles get twitchy, I take a magnesium supplement. Sometimes it helps to take magnesium/calcium/zinc just to be on the safe side.