You are seeing a 45-year-old male in A&E who has presented with a headache and a low-grade fever. During the history, the patient reports to you that for the last few days he has been experiencing nausea, vomiting, abdominal pain, a craving for salt, muscle weakness and dizziness. On examination you note that this patient has hyperpigmentation in the palmar creases and mucous membranes. He has a past-medical history of type 1 diabetes and hypothyroidism. What is the most likely diagnosis?