Three years after a mysterious illness nearly drove her insane and took her life, Susannah Cahalan visits a patient with the same rare, dangerous condition.

Susannah Cahalan is the New York Times bestselling author of "Brain on Fire: My Month of Madness." She began her investigative reporting career at The New York Post when she took an internship her senior year of high school. She has now been at The Post for ten years, three of which she worked full-time after graduating from Washington University in St. Louis. Her work has also been featured in The New York Times, Scientific American, and Glamour UK.

This story originally aired on June 30, 2013.