By Emily Mitchell/Reported by Wendy Cole

Costochondritis. Nearly unpronounceable, that's the name of the mystery ailment that sent Michael Jackson to the hospital with chest pains. The inflammation of cartilage in the front part of the ribs, said the doctor who treated the singer, "can be caused by overexertion and stress." Early last week Jackson collapsed at his Los Angeles home after a two-hour dance workout. Besides being under pressure to finish his new album--the first since 1987's megahit Bad--Jackson, 31, has had some recent personal traumas, including the deaths of his grandmother and his close friend Sammy Davis Jr.