Sleepwalker

The name mixup is the first sign that Sarah's identity is fractured. She is actually Anna Wells, the obsessive fan who shot Jonathan Grey. Due to partial retrograde amnesia, she believes she is Sarah Foster, the woman Jonathan was truly with. The doctors and paperwork reflect her real identity (Anna Wells), which is why she appears confused about the name discrepancy.

Earlier scenes show her documents listing her as Sarah Wells, and Koslov references a dream form that she does not remember writing.

Jonathan was murdered, not a suicide as Sarah believed. Anna Wells, his obsessive fan, shot him. Sarah discovers this truth when reading her diary, which reveals the actual events. This revelation reframes her entire understanding of her past and her relationship with Jonathan.

The film hints at this early on when Sarah learns about selective memory loss and partial retrograde amnesia, suggesting her memories of Jonathan's death may be false.

Warren Lambert is the stalker pursuing Sarah throughout the film. He is the dark-haired man who chases her and makes threatening phone calls. White suggests that the stalker might be the key to linking Sarah's two competing realities of dream and waking life. His attacks trigger Sarah's memories to resurface.

The dark-haired man appears multiple times chasing Sarah before his identity is revealed.

Sarah is actually Anna Wells, an obsessive fan who was obsessed with Jonathan Grey. She shot him and then fell into a coma. When she woke, she suffered from partial retrograde amnesia, believing herself to be Sarah Foster, Jonathan's real partner. The film blurs reality as she slowly recovers these buried memories.

Throughout the film, she encounters the woman from her dreams who feels all too real, this woman is part of Anna's own nightmare.

Dr. Cooper originally knew Sarah Foster, the real woman who was with Jonathan Grey. When Anna (believing she is Sarah) approaches Cooper, she appears as a stranger because Anna Wells is a different person entirely. Cooper's lack of recognition is one of the first major clues that Sarah's sense of identity is fundamentally wrong.

Earlier, Cooper suggests the sleep clinic stay, but later does not recognize her, signaling something is wrong with her identity.

Sarah discovers that Jonathan was murdered, not that he committed suicide as she had believed. The diary contains the truth about his death, revealing that Anna Wells shot him. This discovery is the turning point that helps her begin piecing together her fragmented reality and true identity.

The diary revelation comes after White suggests the stalker might connect the two realities.

Sarah's sleepwalking is caused by her psychological trauma and partial retrograde amnesia. As Anna Wells dealing with the guilt of murdering Jonathan, her mind created a false identity (Sarah Foster) to cope. The sleepwalking represents her mind trying to process and reconcile these competing identities and buried memories.

After Jonathan's suicide, her sleepwalking begins, showing the trauma triggering her dissociative state.

The two competing realities exist because Sarah (Anna) is experiencing a dissociative state caused by her amnesia. She switches between her constructed identity as Sarah Foster and fragmented memories of her life as Anna Wells. The sleep clinic, the strange house, and the shifting roommates represent her mind blurring the lines between her fabricated past and actual history.

Her first night at the clinic shows her waking in a different room, establishing early that her perception of reality is unstable.

Anna Wells and Sarah Foster are two separate women. Anna is the obsessive fan who shot Jonathan Grey. Sarah Foster is the woman Jonathan was actually in a relationship with. Due to Anna's partial retrograde amnesia, she believes she IS Sarah Foster. The entire film takes place inside Anna's fractured mind as she slowly uncovers this truth.

The woman Sarah sees in her dreams, who feels terrifyingly real, is actually herself as Anna.

The ending confirms that Sarah is Anna Wells. She shot Jonathan out of obsession, then fell into a coma. When she awoke with partial retrograde amnesia, she constructed a new identity as Sarah Foster, the woman Jonathan actually loved. She has been living in a delusional state, mistaking her own past for someone else's life, trapped inside her mind's nightmare.

Her dreams of suffocation and being trapped in plastic represent her coma state and inability to breathe under the weight of her stolen identity.