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. 

 This just published study should be of interest to you

Very positive about the effect of Ketosis on the kidneys

https://drc.bmj.com/content/12/2/e004101.info