What are your favorite 'descent into madness' films?

What are your favorite descent into madness films? Movies where the main character slowly loses their mind as time goes on. Mine would be..Perfect blue - the main character loses her grip on reality. The films editing makes it feel what shes feeling.Repulsion - the main character slowly looses her mind in her apartment after her sister leaves her alone. She begins to hallucinate and becomes violent. It has amazing black and white cinematography and atmosphere.The babadook - I love how the monster itself represents her grief. And how she slowly starts hallucinating and loosing her sense of time.What are some of yours? via /r/movies https://ift.tt/2ETJaOg