"Whitney got extremely upset and said she felt the walls were closing in on her," a source close to Houston said in Wednesday's New York Daily News.
Houston left the center Saturday afternoon for an undisclosed location near her Atlanta home, said Nancy Seltzer, Houston's spokeswoman.
"Miss Houston is continuing the prescribed treatment, as was planned," Seltzer said. "Her movements are in total keeping with the program."
Houston admitted in December 2002 to abusing liquor, marijuana, cocaine and pills but said she had kicked her addiction with the help of a spiritual adviser.
The adviser, Prince Asiel Ben Israel, told the CBS News program "The Early Show" on Tuesday that Houston is hooked on prescription drugs, not marijuana and cocaine.
"When you've got the demands of the press and the demands of your public, you're trying to take a pill to stay up and one to lay down," he said. "I think it's that kind of lifestyle."