I've been ketogenic for most of the last two years, mainly to control insulin resistance.

It is VERY common to have problems with low electrolytes in the first few weeks of a LCHF diet. Insulin causes one to hold onto electrolytes and thus retain water. Once insulin needs go down, electrolytes are lost. Symptoms of low sodium include headaches, weakness, fatigue, nausea, BM issues, brain fog, muscle aches, and eventually muscle spasms (once your sodium has been low long enough for potassium to be leeched out and used as an electrolyte).

A ketogenic diet often (usually) seems to require that one gets 3000-5000 mg of sodium per day. There is 2300 mg of sodium in a teaspoon of table salt so that is roughly 2 teaspoons of salt per day. You can get that with salted food and water, broth, or salt tablets.

Potassium will go low if sodium needs are not addressed. Many supplement with K. Magnesium can help too although too much Mg can affect BMs.

The Low Carber Daily MFP group has a lot of good information on that in their stickies / launch pad.

Especially first couple weeks of keto, it is *extremely* common to have "keto flu" which is a sodium/potassium deficiency.