We need more sodium on a ketogenic diet, because without all those carbohydrates to stimulate insulin, the kidneys are no longer being prevented from excreting sodium at the proper rate. Those symptoms you mention are merely signs of lack of salt. Cook with more salt, put a little more on your food, eat bacon—you’ll find a way to get enough salt. The good news is that when we get enough salt, that usually also keeps our potassium, magnesium, and calcium at healthy levels, since the regulatory mechanisms for these minerals are all interlinked.
Constipation is another symptom of lack of sodium, so if I forget to keep my salt up one day, I’ll be reminded the next. If I should happen to overdo it, the effect is also noticeable, lol! (I’ll spare you the details.) You’ll figure it out.
A note, however: Even with the salt taken care of there is a period of what we call fat-adaptation, as the muscles stop metabolising sugar and re-learn to metabolise fatty acids instead. But in the meantime, they are limping along on the ketones your liver is producing, and you may find there’s a limit to how well you perform on your workouts. This normal and temporary, and it passes in six to eight weeks. The adaptation process is gradual, but one day you’ll realise just how much you’re accomplishing.
For me, it wasn’t so much a lack of energy per se, so much as a limit on how much force I could exert with my muscles. Nowadays I am not only stronger, but I have much more stamina than I used to. I contracted some sort of undiagnosed fatigue syndrome in 2006, as the result of a bad viral infection. It used to be that any exertion above the minimum necessary to go to work would lay me up for a couple of days; now I can mow the lawn for four or five hours, say, and still be functional. For me, that is a huge blessing.