Syndrome of inappropriate ADH secretion.
Too much ADH
Too little urine (anti diuretic), highly concentrated urine, reabsorbing too much water, too dilute plasma
Look out for CNS diseases (CNS tumour, trauma, stroke etc),chronic Lung diseases (Lung tumour, TB) or medications (vincristine, vinblastine)
Treat primary cause
If no response, induce nephrogenic DI with Lithium or Demeclocycline.