"Before I Go to Sleep" is a psychological thriller novel by S.J. Watson. It follows the story of Christine Lucas, a woman who loses her memory every time she falls asleep due to a traumatic incident. Each day, she wakes up without any recollection of her past, relying on her husband, Ben, to help her piece together her life. As Christine keeps a journal to document her daily experiences, she begins to uncover unsettling truths about her past and the people around her. The narrative explores themes of memory, identity, and trust, creating a tense atmosphere as Christine seeks to understand her reality.