Chronic hyponatremia is often called asymptomatic hyponatremia in clinical settings because it is thought to have no symptoms; however, emerging data suggests that "asymptomatic" hyponatremia is not actually asymptomatic.Acute hyponatremia is when sodium levels drop rapidly, resulting in potentially dangerous effects, such as rapid brain swelling, which can result in coma and death. Treatment
The treatment of hyponatremia depends on  the underlying cause. How quickly treatment is required depends on a persons symptoms. Fluids are typically the cornerstone of initial management. In those with severe disease an increase in sodium of about 5 mmol/L over one to four hours is recommended. A rapid rise in serum sodium is anticipated in certain groups when the cause of the hyponatremia is addressed thus warranting closer monitoring in order to avoid overly rapid correction of the blood sodium concentration. These groups include persons who have hypovolemic hyponatremia and receive intravenous fluids (thus correcting their hypovolemia), persons with adrenal insufficiency who receive hydrocortisone, persons in whom a medication causing increased ADH release has been stopped, and persons who have hyponatremia due to decreased salt and/or solute intake in their diet who are treated with a higher solute diet.
Cirrhosis of the liver
Congestive heart failure
Nephrotic syndrome in the kidneys
Excessive drinking of fluids

Normal volume
There is volume expansion in the body, no edema, but hyponatremia occurs
SIADH (and its many causes)
Hypothyroidism
Not enough ACTH
Beer potomania
Normal physiologic change of pregnancy
Reset osmostat

Low volume
Hypovolemia (extracellular volume loss) is due to total body sodium loss. Hyponatremia is caused by a relatively smaller loss in total body water. Any cause of hypovolemia such as prolonged vomiting, decreased oral intake, severe diarrhea
Diuretic use (due to the diuretic causing a volume depleted state and thence ADH release, and not a direct result of diuretic-induced urine sodium loss)
Addisons disease and congenital adrenal hyperplasia in which the adrenal glands do not produce enough steroid hormones (combined glucocorticoid and mineralocorticoid deficiency)
Pancreatitis
Prolonged exercise and sweating, combined with drinking water without electrolytes is the cause of exercise-associated hyponatremia (EAH). It is common in marathon runners and participants of other endurance events. The use of MDMA (ecstasy) can result in hyponatremia. Medication
Antipsychotics have been reported to cause hyponatremia in a review of medical articles from 1946 to 2016.Available evidence suggests that all classes of psychotropics, i.e., antidepressants, antipsychotics, mood stabilizers, and sedative/hypnotics can lead to hyponatremia. Age is a significant factor for drug induced hyponatremia. Other causes
Miscellaneous causes that are not included under the above classification scheme include the following:

False or pseudo hyponatremia is caused by a false lab measurement of sodium due to massive increases in blood triglyceride levels or extreme elevation of immunoglobulins as may occur in multiple myeloma.