அந்நியன் (தமிழ்) / अपरिचित (हिन्दी) / Aparichit

This movie talks about what was formerly known as split-personality, or multiple-personality disorder, but is now known as dissociative identity disorder. The reason for this is that there are different traits of perception and response in a single individual in different circumstances than otherwise highly distinct personalities. This condition is very rare and there have been only 50 documented cases worldwide. As the name of the movie suggests, "Aparichit" in Hindi literally means "someone who has not been introduced to himself".

The protagonist in this film is a lawyer, who is shown to be a brutal murderer according to sacred Tamil texts of punishments given in hell (please correct if I'm wrong - no offence), and a lovey-dovey lover in another personality. The film is in Tamil, although I've watched it in Hindi as I do not understand the former language. The cinematography is surreal with time freeze done a couple of times.

The biggest mistake in this film is that the protagonist's E.E.G. was not done during evaluation, and he shows a lot of eye movement in the murder scenes, both of which could suggest epilepsy. Also, the suggestions for improvement of the patient made by the doctor are to some extent nonsensical and unprofessional. That aside, the film truly depicts dissociative-identity disorder. 

P.S. - Not for the faint-hearted