Mental imagery
The imagery of body and mind defines Cahalan's point of view. She is not someone who ever gave that such direct attention. It is not like she was studying the brain or something. She is working for a newspaper and dating someone she really likes, embedded in the daily narrative imagery of her life, and then suddenly, an inciting incident happens and she loses all memory and much of the normal function of her brain. Suddenly, she has an experience of mind which is jarring and inconsistent with her sense for normalcy. The concrete imagery is a mystery until it is solved by medical professionals; without that concrete anchor, the change in brain performance came at a great price. It is difficult to define what that sublime imagery was like really for her, but she writes about intense episodes of psychotic panic and fugue states.
Medical imagery
The imagery of doctors and medicine is an important part of this memoir's drama and action. To get a sense of how this imagery really works in the memoir, just imagine that without context, you suddenly wake up in a white building with lots of strangers who are poking and prodding you. In Susannah's case, that came with a great deal of memory loss in general, so imagine how minimal her framework for understanding her state was. Without memory, the medical imagery can be very puzzling indeed, and without memory, it would be difficult to be calm.
Immune system imagery
Because of the nature of Susannah's illness, the memoir takes on a poignant imagery of the body. Instead of taking the imagery of the body for granted, Susannah is made unequivocally aware of her body's bio-mechanical nature. It is "malfunctioning," as it were. This leads to a medical experience that can be described by frustration and confusion, because her illness is that her body believes it is ill in ways it is not ill, and by "treating" problems that are not real, the body sacrifices its own performance. In this case, it is to an extreme level so that without explanation, Susannah's community watches her slowly go insane as her immune system alters her brain function.
Survival and healing
The imagery that defines Cahalan's memoir is not suffering. It is survival. By outlasting her illness with the help of skilled medical professionals, Cahalan lives on to create a new identity in spite of her illness. That is an outcome which probably came with great catharsis, considering the emotional confusion and sorrow that Cahalan endured. By not having memory, she also lacked the context to make sense of her daily life, and the tragedy of her downfall would have been a sorrowful legacy if she had died. By surviving, she becomes a hero of healing and hope.
