a) sodium might help draw water into muscles, which would help strength a bit. It's also an electrolyte (along with potassium and magnesium), which can help your brain feel less foggy if low blood sugar is getting to you. Plus, it adds flavor to bland food. If you don't have high blood pressure, I vote to toss some sodium in there. Or Lite salt, which is half sodium half potassium.
b) no idea. Maybe you've built up a tolerance?