I have several small handfuls of salt every day & my serum sodium level still is on the low side of normal or slightly below. i black out and im dizzy if i dont get that much salt and fluids. what could cause that? my cortisol level was normal

If your kidneys are normal, salt will not elevate your blood sodium levels, assuming you're not ingesting truly giant amounts. Sodium levels in blood are primarily modified, when necessary, by increasing or decreasing fluid intake. Discuss this with your doctor. In the meantime, eating extra salt is not likely to either raise your sodium level or improve these symptoms.