Twenty-one-year-old Susannah Cahalan is an acclaimed writer for The New York Post, sharing her life with her new boyfriend, Stephen Grywalski. Suddenly, Susannah falls ill, beginning with symptoms akin to an ordinary flu, such as a persistent cough and overwhelming fatigue. However, her condition takes a bizarre turn as she exhibits peculiar behaviors during trance-like states, including hearing voices that aren't spoken and an aversion to loud sounds.
As her erratic conduct intensifies, a seizure prompts her to seek medical assistance. The attending doctor dismisses her symptoms as mere exhaustion from partying too much and overworking. To find respite, Susannah moves in with her mother, Rhona Nack. Following an emotional breakdown, she suffers another seizure, leading to her admission into a medical facility for an MRI. In her mind, she grapples with the possibility of having bipolar disorder due to her drastic mood swings.
Caring for Susannah proves challenging for Rhona, eventually leading her to reside with her father, Tom Cahalan, and his fiancée. One fateful dinner escalates into violence during one of Susannah’s outbursts, which prompts her parents to insist on hospitalization despite normal results from various tests including MRI and EEG. Within the hospital, one doctor proposes the unsettling possibility of schizophrenia, warning that if Susannah's condition does not improve, she may need to be moved to a psychiatric unit.
As time passes, Susannah’s condition deteriorates to a catatonic state, prompting her parents to enlist the help of Dr. Najjar, who undertakes an investigation into Susannah's case. In a pivotal moment, he asks her to draw a clock; the result is alarming as all numbers are situated on one side, suggesting swelling in the right hemisphere of her brain. A brain biopsy is undertaken, and the results reveal a rare condition known as anti-NMDA receptor encephalitis—an inflammation of the brain that Dr. Najjar poignantly describes as “a brain on fire.” With this diagnosis, he commences treatment that facilitates her gradual but full recovery.
Fast forward seven months, Susannah triumphantly returns to her job and presents her first article since regaining her health to her boss, Richard. The article garners praise, leading him to encourage her to pen a memoir about her harrowing experiences, which she aptly names Brain on Fire. The film concludes with the impactful text that Susannah Cahalan was the 217th individual to receive a diagnosis of anti-NMDA receptor encephalitis; her memoir has since illuminated the paths for many others, resulting in thousands being diagnosed and treated subsequently. Today, she maintains a close friendship with Dr. Najjar, a testament to their journey together.
