ABC News' Paula Faris contributed to this report:

Nearly 5,000 flights go through her airspace each day, but it was a twin propeller plane on its way from Dallas to Michigan last November that alarmed Louella Hollingsworth.

Sensing there was something off with the pilot, Hollingsworth responded by asking the pilot to lower the altitude of his plane.

"November, five, zero, one, papa, mike," Hollingsworth is heard saying on the recording. "I think you need to start a descent. Can you do that for me, descend and maintain flight level two, four, zero?"

Image credit: ABC News

All Hollingsworth heard on the other end was heavy breathing from a pilot soaring at 27,000 feet in one of the country's busiest airways.

Heavy breathing is a tell-tale sign of hypoxia, or lack of oxygen, a condition that causes shortness of breath and can render individuals unconscious, eventually causing death if oxygen levels in the body are not restored to normal.

"I didn't know if he'd ever answer me again," Hollingsworth told ABC News.

An exchange ensued between Hollingsworth and other pilots until the distressed pilot became more responsive, eventually descending to 14,000 feet, an altitude safe without cabin pressure for short periods of time, according to the Federal Aviation Administration.

Last week, Hollingsworth was one of a dozen individuals who were honored by the National Air Traffic Controllers Association with its Medal of Safety award for her assistance in saving the pilot.