A 72 year old woman who had a repair of strangulated femoral hernia 2 days ago becomes noisy, aggressive and confused. She is afebrile, CBC normal apart from raised MCV. What is the most likely diagnosis?

The key is B. Delirium tremens. [Electrolyte imbalance may cause confusion but not aggressiveness; infection toxicity will cause high fever, low BP, rash etc which are absent here. Abstinance from alcohol in the hospital caused delirium tremens (chronic alcoholism is supported by high MCV) here].