The following day, Dr. Khan, a psychiatrist, arrives to evaluate Susannah. She notes Susannah's disheveled appearance, as that can be a sign of mania or a psychotic break. Susannah informs Dr. Khan that she has dissociative identity disorder, a condition where a person has multiple distinct and separate identities. Susannah describes being diagnosed as bipolar, but refusing to take her medication. She also says that the hospital isn't safe, she needs to escape, and everyone is making fun of her. Dr. Khan diagnoses Susannah with either an unspecified mood disorder, an unspecified psychotic disorder, or bipolar disorder. She also suggests that there might be an underlying disease and recommends that Susannah be assigned a security guard to prevent further escapes.
Again, as Susannah attempts to diagnose herself, she tries to make sense of her identity by giving herself the language to describe it in terms of illness. Though from a theoretical standpoint, dissociative disorder makes some sense (Susannah is absolutely not the person she was, and insists she has separate pre- and post- identities), from a medical standpoint it's nonsense. It's worth noting that these unspecified disorders are the kinds of diagnoses that could land Susannah in an institution. Though they're a diagnosis, they don't tell a full story of what's going on.
Susannah describes a hallucination in which she looks at a doctor's face and the face ages before her eyes. She turns to Stephen, who also appears to age. When Susannah turns back to the doctor, the doctor suddenly grows younger until she looks like a teenager. Susannah feels as though she has a special power.
Not all of Susannah's hallucinations are terrifying, which suggests that some of her paranoia might be receding. Metaphorically, seeing Stephen age connects to how he drastically matures and changes during this time in the hospital.