Signs of trouble were apparent days before the Tuesday morning arrest of Robert Downey Jr., 36, reports PEOPLE in its latest issue. "He was sweaty and shaky and didn't know his lines," says one source from the set of "Ally McBeal," on which the troubled actor costarred -- until producer David E. Kelley announced on Tuesday, only hours after Downey's arrest, that the rest of the season would be finished without him. "But they've had to scrap everything and start over." What started the actor's emotional tailspin? A source tells PEOPLE that it began when Deborah Falconer, who has filed for divorce from Downey, said she was going to move to New York and take their son, Indio, born in 1993, with her. As for Downey's current state of mind, "devastated would be a good way to put it," says an acquaintance. Shortly after midnight on April 24, Culver City, Calif., police arrested Downey, whose hyperactive behavior and dilated pupils led them to believe he was under the influence of drugs. "He was cooperative," the magazine quotes Lt. Dave Tankenson as saying, "but somewhat somber and disappointed." Immediately following his arrest, Downey entered an L.A. detox facility after which, says a state Department of Corrections spokeswoman, he will be sent to a live-in drug rehab center.