I need a good psychological thriller mind fuck to watch. Any suggestions?

I want to watch a movie where the main character slowly goes through some mental change throughout the movie and be a totally different person by the end of it. I also want to be confused for 90% of it. Something that really makes me think about it after I've seen it. Any suggestions are greatly appreciated!

Edit: I didn't expect to get so many comments. Thank you to everyone that gave me recommendations!