We do need the Salt. 6 gram of Sodium Chloride a day on average. There’s good reason people risked their lives crossing deserts for Salt. 

The “Keto flu” a few days in on low carb is because we stop retaining it and start peeing it out causing Orthostatic Hypotension which results in light headedness when standing, headaches and a general feeling of weakness and low mood. 

Keep all your electrolytes up and I found it’s much easier to fast or stay low carb.