Can Plain Salt Ever Cure Backaches?

I'm on a low salt diet. This is only because I take meals with my father, who has a condition. Based on my own blood tests, I don't really need to avoid salt myself.

For the last few months I noticed that my lower back muscles are tense and guarded by the end of a workday. At the absolute worse I had spasms. Usually it just aches and needs to be stretched out a bit. I also used to get a thigh pain that I think could have been a pinched nerve. Anyhow, I've done a lot of experimenting. Decompression exercises help. I've read a little about herniated discs. I'm fine biking, walking, or swimming, but standing too long can set me off. Then I discovered something really odd.

Ordinary table salt NaCl is the cure. Get a little salt at lunch, and I'm fine all afternoon.

I have read that salt deficiency can cause muscle aches, but is the really a thing? Is it normal or rare? Any info?