I agree with you NH.
whatever experience you have had in alleviating symptoms of back pain and so on with salt, it is most definitely a false one, perceived or not.
I suggest you read this article very thoroughly to have an accurate picture of which sodium you need and do not need. http://www.drfuhrman.com/faq/question.aspx?sid=16&qindex=1
It is possible that you may have been deficient in sodium before the commencement of your fast.
You will enter "starvation mode" if you continue with taking salt or any other form of nutrient even in small quantities.
I'll give you one example here: if you live on a Vitamin C deficient diet, then you will develop scurvy, but on a water-only-fast scurvy does not develop because your nutritional reserves are preserved for as long as possible.