A total mind fuck.
If you haven’t seen the movie and is interested, dont read this.
If i’m being honest, i would probably had the idea that Teddy (or maybe Andrew) was one of the insane patient, because i accidentaly saw a bit of a spoiler.
But if i didn’t see that little spoiler, i would probably said that i know that Teddy was insane when he had a dream meeting Andrew laeddis. I think that dream is supposed to be a metaphor to Teddy meeting his real self (Andrew) which he depicts as a murderer and a total psycho. This later on was proven when the head psychiatrist John cawley said that andrew killed his wife after she killed his children, he later on felt extreme regret and ended up making delusions to escape from his reality, leading him to went insane and ending up in the shutter island.
His delusion was him being a US marshal investigating the disappearance of Rachel solando, which later was revealed that YES IT WAS HIS DELUSION, Rachel solando wasn’t a missing patient, Rachel solando was his delusion about a lady that killed her own children and went insane (just like his wife Dolores chanal). His partner Chuck was not his partner, IT WAS HIS PSYCHIATRIST. All this time he thought he was a US marshal investigating a missing patient but turns out he was in a big role play planned by the doctors in order to cure him. Damn, a very depressing movie.