A 58-year-old woman complains of dizziness, weakness, and losing 14 kg within 2 months. The patient has a past history of tuberculosis. Objectively, she presents with increased skin pigmentation, body weight deficit of 10 kg, and blood pressure of 90/55 mm Hg. Blood test revealed the following Na - 117 mmol/L, K - 6.4 mmol/L, CL - 116 mmol/L, [HCO₃] - 27 mEq/L, glucose - 2.9 mmol/l. What is the most likely diagnosis in this case?