(sorry for my bad English in advance)
I saw this movie 5 years ago! There was serial killer who kidnaps people and put them in big water tanks build inside his house which inside attached with a surveillance camera !! That killer was having a mental illness. When police caught him he was taken for treatment to psychologic doctor and then the doctor asked to get inside the mind of the killer to get to know what happening inside .. Once the doctor get inside the mind she sees very psychedelic trippy scenes inside his mind! (like goat was kept in a cage an crushed inside the cage with thorns)
If the doctor can’t able to return in certain time she will trapped inside the mind of the the killer!!