Low serum sodium (<135mmol/L)
Diuretic excess— especially thiazides
Renal failure
Nephrotic syndrome
Diarrhoea/vomiting
Small bowel obstruction
SIADH
Water overload (e.g. polydipsia)
Severe hypothyroidism
Addison’s disease
Glucocorticoid deficiency
Cardiac failure
Cirrhosis
Confusion
Lethargy
Personality changes
Convulsions
Coma
Death
Treat the underlying cause