Severe hyponatremia or severe symptoms (confusion, convulsions, or coma): consider hypertonic saline (3%) 1–2 ml/kg IV in 3–4 h. Hypertonic saline may lead to a rapid dilute diuresis and fall in the serum sodium. It should not be used in those with an expanded extracellular fluid volume.
If your hyponatremia came on suddenly and it’s severe, you may need to get fluids by IV so that you can get sodium quickly. You may need to stay in the hospital. If you have symptoms like headache, nausea, or seizures, your doctor may also give you a prescription to keep these problems under control.
A possible explanation for how hyponatremia causes muscle cramps in athletes is that, after losing a lot of salt and water through sweat, dehydration and lack of salt make the spaces between the muscle cells contract, increasing pressure on the nerve terminals and causing pain, states the BBC.
Low volume hyponatremia can occur from diarrhea, vomiting, diuretics, and sweating. Normal volume hyponatremia is divided into cases with dilute urine and concentrated urine. Cases in which the urine is dilute include adrenal insufficiency, hypothyroidism, and drinking too much water or too much beer.