As trevyn says, you need to make sure you get enough sodium. Ketogenic diet accelerates excretion of sodium ("natriuresis of fasting"). Look up Steve Phinney's

As trevyn says, you need to make sure you get enough sodium. Ketogenic diet accelerates excretion of sodium ("natriuresis of fasting"). Look up Steve Phinney's videos or books if you want more info -- he recommends drinking a few full-sodium stock cubes every day. Another common issue during adaption seems to be not eating enough fat.