A 20-year-old Irvine man, federally charged with the assault of a crew member aboard an American Airlines flight last week, told investigators he was acting in self-defense after flying home from brain surgery. According to an affidavit obtained by Denver7, Brian Hsu claimed he suffers from psychological damage stemming from an assault in New York City last year, including a “mental fog” that impedes his ability to think clearly.

Earlier on Monday, Hsu was arrested by the FBI after “one of the worst displays of unruly behavior we’ve ever witnessed,” according to American Airlines CEO Doug Parker. In the affidavit, Hsu claimed he was stretching outside the lavatory on the Oct. 27 flight when he accidentally bumped the flight attendant, who “became agitated and began swinging” at him. Hsu told investigators he was scared that “an impact to his head in its current state could cause him severe injury or death,” so he raised his hands in defense. The attendant then “charged at him and hit her nose against the palm of his right hand.”

Witnesses interviewed by investigators commented on Hsu's “odd behavior,” according to the affidavit, and that Hsu punched the attendant in the face, leaving her with a fractured nose. He appeared briefly in U.S. District Court for the Central District of California on Monday to be charged with interference with a flight crew and assault within the special aircraft jurisdiction of the United States.