SODIUM, linked with chloride in the form of sodium chloride, works hand-in-hand with potassium to promote nerve conduction, and hence, life sustaining processes. By adjusting levels of intra- and extracellular sodium levels, the body attempts to maintain optimal blood volume. Too high a blood volume results in hypertension (high blood pressure), while too low a blood volume results in hypotension (low blood pressure).
A deficiency of sodium chloride (salt) is not usually due to low salt levels in the diet, but rather from excess sweating (sports, physical work, heat, etc), as well as vomiting and diarrhea. There would be symptoms such as fatigue, muscle cramps, nausea and vomiting, headaches, disorientation, and fainting. Sudden, severely low levels of sodium chloride might result in brain swelling, seizures, coma, and brain damage, potentially leading to death.
Under normal circumstances, we are much more concerned with excess intake of salt, leading to hypernatremia (high levels of blood sodium). Excess sodium may lead to low levels of calcium (and osteoporosis), kidney stones, and hypertension. Hypertension may result in damage to the inner organs by reducing optimal blood flow to them. Blood brings oxygen and nutrients to all tissues in the body, and removes carbon dioxide, as well as toxins.