A 55 year old man, a chronic smoker is brought to emergency with history of polyuria, polydipsia, nausea and altered sensorium for last two days. He had been diagnosed as having squamous cell carcinoma of lung two months prior to this. On examination, he was lethargic and confused. An ECG was normal except for a narrowed QT interval. Which one of the following is the most likely metabolic abnormality ?