Fight Club (1999) Trailer:
The psychological-thriller genre focuses on the unstable emotional state of characters combined with mystery and thriller. Psychological thriller often involves aspects from mystery and drama genres, but can also involve traits from horror. Too many aspects from horror though can cause the film to become a psychological-horror.
The cliche of a psychological-thriller is usually the main character having to overcome an enemy using mental strength, as opposed to physical. This enemy could be another character who's using deceptive mind games to control them, or the enemy could even be an internal conflict that they must overcome. It's seen that the character will usually be in as bad mental state at the beginning and/or middle of the film, but at the end will have concurred their problem and recovered.
A back-story is used in the genre lots to be the reason why a character is mentally unstable. The back-story is revealed at one point to deepen our understanding of the story and character. This is great for plot-twists and character development.
A first person narrative is also used frequently in this genre so we see from the character's view point and enables the audience to understand the mental state and to become involved with this character. This technique can also be pared with the technique of unreliable narrator. The reason is for plot twist that make the film more exciting, psychyological and thrilling.