If you’re someone who loses a lot more, you’ll probably see and feel salt stains or crusts on your clothing or face when you’re training hard, especially in the heat. You also probably don’t like training in the heat very much because it does make you feel a bit crappy. You might get cravings for salt, it might sting in your eyes or if you get a cut, your sweat will sting.
You might also suffer with low blood pressure from time to time, especially post-exercise, because sodium keeps your blood volume up. As you put more sodium into the blood, your body puts more fluid into the blood plasma to dilute it down and that keeps your blood pressure up. So if you lose lots of salt in your sweat quite often there’s a contraction of your blood volume, and that leads to that lightheaded dizziness you feel when you stand up quickly after you’ve been exercising.