Before I Go to Sleep is a psychological thriller. The genre is characterized by a protagonist (often the narrator) who experiences extreme emotional turmoil. The conflict in a psychological thriller often stems from the main character’s tenuous grasp on reality. They distrust others but, at the same time, feel their own perception is unreliable. An atmosphere of foreboding, suspense, and paranoia is created as the protagonist battles to discover a truth that may put them in danger. Standard literary techniques of the genre include plot twists, an unreliable narrator, red herrings (clues designed to misdirect the reader deliberately), and complex plots.

Watson’s novel can also be categorized as domestic noir, a subgenre of the psychological thriller that focuses on conflict within the domestic sphere. Home is portrayed as a potentially dangerous environment for the protagonist. The main character (usually a woman) is often subjected to escalating psychological abuse, such as gaslighting and coercive control.

In Before I Go to Sleep, Watson combines psychological tension with an atmosphere of domestic noir through his use of an amnesiac narrator. Christine’s memory loss makes her narrative potentially unreliable and limits the information she can convey to the reader.