My impression of the movie is that half is the “reality” happening while the other half is a sexual fantasy while she is masturbating. When she can’t get off the nightmare of her reality crumbles and she can’t go on. Its a movie that needs to be seen through a mind fog, like most David Lynch movies. Once you allow him to dictate the rules of how the movie is going to presented to you, then you see the beautiful things that he creates with film.