So what REALLY happened here?

Many psych-thriller films have endless theories and interpretation, such as Memento and Inception, yet for whatever reason this film gets way less attention than it deserves, considering the complexity of the plot.

So does anyone have any theories they would like to contribute, as to what is actually going on in this film?

At face value, this film is about Dae-Su's revenge. But there are some unanswered questions.

I read a theory here that says that Dae-Su only exists in the mind of Woo-Jin, as he is the "monster" of his past that led to his sister's death:

http://endofthegame.net/2011/08/27/oldboy-an-interpretation/

But when I watch this film, for some reason I get a strong feeling that there is a temporal loop happening, such as in Mullholland Drive, or Shutter Island. Hear me out.

Near the beginning, we see that Dae-Su starts writing down things that he says was his "evil past." Why no mention of this past? It is only brought up again when Woo-Jin says that Dae-Su simply "forgot" the rumor that he started, he only becomes apologetic when he realizes that Woo-Jin will reveal the secret about Dae-Su to Mido. Later, he gives the letters that he presumably wrote earlier to the hypnotist who appears earlier in the film.

Now there is a question regarding the flow of time in this film, since he spent 15 years turning regret into revenge and back into regret again. The theme of hypnosis is strong in this film, we are to believe that Mido and Dae-Su were hypnotized into falling in love with each other, unaware of their father-daughter relationship.

I believe that this entire film takes place in Dae-Su's mind, as opposed to Woo-Jin. A big clue is that we see the hypnotist towards the beginning and end of the film. What if they were not separate sessions, but rather the entire film was one long trance?

In the beginning of the film, Dae-Su disappears after getting drunk one night. Instead of getting kidnapped by mobsters, what if he actually went into a fugue state, or even started having paranoid delusions?

The "jail" he was in is actually a psychiatric hospital, the "sleeping gas" are his sedatives whenever he goes into psychosis. Remember the ants? He is always "dragged away" after he passes out from his hallucinations. Where is he being taken? To some procedure? The "hypnotist" is his psychiatrist, and all the events that unfold in the film are him coming to terms with his own delusions and paranoia.

His wife was never actually killed, but is estranged, he believes that his daughter is "pure" which is why she was "sent" to sweden, he refuses to accept his incestuous attraction to his daughter, which is why he creates the elaborate rumor about woo-jin and his sister. Remember when mido gave a strange look to the shopkeeper when she was telling her about Dae-Su's daughter? She knew that something was strange.

On a deeper level, the "jail" represents Dae-Su's mind, how he is trying to "break free" from the dissonance in his mind, the TV represents the stream of consciousness from his false reality; constricted and filtered. He has "trapped himself" there because he cannot deal with his dysfunctional family life, only the hypnotist could "free" him.

Woo-Jin represents Dae-Su's paranoia- which possibly alludes to schizophrenia. Dae-su constantly believes that he is being "watched, listened to," etc. Only when Woo-Jin is dead, can the "monster" be freed- the monster that was created by Woo-Jin.

The ending confirms that Da-Su was stuck in his hypnosis all along, as evidenced by the diary and the Hypnotist, but he is in a snowy forest, representing the "coldness" of his realizations, he will never be able to express his incestuous love for his daughter.

Sorry if it is long and disorganized, but this movie really had me thinking. Maybe I will update things as I think them through more.