What is the meaning of the expression one's heart dropped to the floor?
It means that someone felt depressed or sad. This is usually
connected to the dashing of someone's hopes and/or dreams, and is
sometimes romantic, but always related to something that is cared
about greatly. If a guy asks a girl to marry him and she says no,
his heart might drop to the floor. If a guy gets a call at work
that his child has been in a car accident, his heart drops to the
floor. That sort of thing.