MRCS-1571

A 60 year old alcoholic man is seen in the A&E department. When asked his reason for being there, he says he is looking for a place to sleep for the night. He is examined by one of the doctors and has no evidence of trauma, a skull x-ray fails to show any evidence of fracture. He is placed on observation and ten hours later, he develops a sudden onset headache, falls into a coma and then dies. What is the most likely cause?