No matter what actually happens in this movie (as it is unclear how much might be real and how much might be delusional), the underlying theme is that mental disturbance is intimately related to difficulties in separating from one's mother due to early life psychological trauma. Of course, this was also the premise of Hitchcock's 1960 film, "Psycho," as well as Sophocles' "Oedipus Rex" back 429 BC.