This story about a frightening incident is narrated in a humorous way. What makes it humorous? (Think of the contrasts it presents between dreams and reality. Some of them are listed below.)
(i) The kind of person the doctor is (money, possessions)
(ii) The kind of person he wants to be (appearance, ambition)

Explanation

(i) The doctor is a poor person. He has hardly any money. he lives in an unelectrified house. It is small rented room with plenty of rats living in it. He has just started his medical practice. So he is not a man of possessions or money.
(ii) The Person wants to be rich. he also would like to have good appearance. That’s why he decides to grow a thin moustache.