Susannah Cahalan investigated her own terrifying medical mystery in the New York Times-bestselling memoir “Brain on Fire: My Month of Madness,” and now Chloë Grace Moretz is depicting the journalist’s harrowing journey in a big-screen adaptation of the book. A newly released trailer for the drama emphasizes just how quickly and dramatically Susannah’s life fell apart.

The 24-year-old is shown positively killing it at her job at the New York Post. “You’re so bright-eyed. I need major sunglasses right now,” a colleague teases. But then she totally botches an important interview, and collapses onto the floor. Doctors tell Susannah she’s perfectly healthy, but she and her loved ones know better. “I’m looking in her eyes and I can tell she’s not there,” Susannah’s mother (Carrie-Anne Moss, “The Matrix”) emphasizes.

Something is terribly wrong with Susannah, and as long as the medical mystery remains unsolved, her health seems to deteriorate.

Check out the trailer for “Brain on Fire” to see how a trailblazing doctor begins to put the puzzle pieces together. The film is written and directed by Gerard Barrett (“Glassland”) and made its world premiere at the Toronto International Film Festival last year. You can catch “Brain on Fire” on Netflix, but the release date is TBA.

Moretz’s recent credits include “The 5th Wave,” “If I Stay,” and “The Clouds of Sils Maria.”