These are common symptoms that can have a very simple cause: a lack of salt. And if so, you can get rid of the symptoms in 15 minutes, by drinking half a teaspoon of salt (about 2 grams) dissolved in a large glass of water. Alternatively have a cup of bouillon (the tastier option).
Salt has probable been too demonized. However, it’s true that excessive salt can raise blood pressure slightly, so if you have high blood pressure you should use this tip with caution.
Under normal circumstances though, and especially on a low-carb diet (that tends to lower blood pressure and increase salt losses), you’re probably going to do better with a moderate amount of salt. Not too much, but not too little either.
If you’re on a low-carb diet and feel low on energy and motivation, tired and unfocused… then consider adding some salt. If you feel much better within 15 minutes it is likely that you were low on salt. If so, you can repeat this tip daily as needed.