When you switch to a low carb diet you tend to need more salt for three reasons:
You are eating less salt from processed foods, low fat foods, bread, ready made sauces, soups etc.
Another action of insulin is to signal your kidneys to retain sodium. So when your insulin levels drop, your kidneys will start to excrete more sodium into your urine than they did before.
You have started drinking a lot more water, you are peeing more often, and you are depleting your glycogen stores which have a lot of water stored with them. So the water balance of your body is changing dramatically. This is closely linked to the electrolytes (sodium, potassium, magnesium etc.) in your body with the result that you lose electrolytes and need to replenish them.
So the upshot of all this is that you need to take more salt (and sometimes more potassium and magnesium too) during the first weeks of going low carb. Long-term you may need slightly more added salt than you used to but you still shouldn't need more than the recommended amount so it isn't a licence to eat loads of salt.
If you're feeling tired, fatigued, headachey, generally lacking in energy then try a salty drink: salt in water, miso (if you can find a low carb one, stock, Bovril (again check the carb count), Oxo cube dissolved in water. If you feel better within about half an hour or so then the problem was too little salt.
If you get cramps, particularly in the legs, then this can mean you need more magnesium. You can get this from magnesium-rich foods or from a supplement. I was dairy-free for over a year so I take Osteocare which has calcium, magnesium and vitamin D.
We used to recommend sea salt, rock salt or pink salt for their electrolyte content but the latest research shows that these aren't effective ways to replenish your electrolyte levels.