Low sodium levels are normal in older people because many have health problems and take medications. My levels (at age 83) have always been borderline. …low normal. Instead of buying sodium tablets I occasionally add some salt to water with lemon juice and gulp that down in the morning especially in the hot humid Florida weather and when I go to my gym classes.
I do try not to limit water because I feel it’s essential to keep hydrated also. I drink this instead of buying electrolyte beverages. You can goggle some of the physical manifestations of very low levels.

FL Mary