Trevor Reznik is an industrial machinist who suffers from severe insomnia and mental deterioration, having not slept for a year. His gaunt and emaciated appearance isolates him from his co-workers, leading to increased suspicion and discomfort in the workplace. Trevor's insomnia and declining mental state cause him to experience hallucinations, paranoia, and a growing sense of unreality. He becomes particularly obsessed with a mysterious figure named Ivan, whom he believes is toying with his sanity. Trevor's only solace comes from interactions with two women—a caring prostitute named Stevie and a kind waitress named Maria.

As Trevor's grip on reality continues to slip, a workplace accident involving a fellow worker, Miller, exacerbates his paranoia. He feels increasingly threatened and begins to uncover a series of cryptic notes and visual clues that suggest a deeper conspiracy against him. Determined to understand what is happening to him, Trevor embarks on a perilous journey into his own psyche, seeking connections and answers. Each revelation brings him closer to the shocking truth behind his condition, forcing him to confront the darkest corners of his mind and the events that led to his current state.