AKT-4544

A 28-year-old woman presents with extreme lethargy at two weeks after the birth of her third child by emergency Caesarean section. After the birth, she needed a blood transfusion. She complained to the health visitor of increasing problems some seven days earlier but was told that this was to be expected after the birth of her child. She has a sodium concentration of 120 mmol/l (135–145 mmol/l), a potassium concentration of 5.6 mmol/l (3.5–5.0 mmol/l) and a urea of 7.5 mmol/l (2.5–6.5 mmol/l.)
What is the most likely diagnosis?