Simpson was performing at MTV's "Cool Christmas" concert in Yokohama, Japan, Friday when she stopped in mid-song and told the audience she was not feeling well.
Although earlier reports said Simpson collapsed in the elevator of MTV Japan's offices, the singer actually returned to her hotel and was taken to an area hospital around midnight local time.
Simpson's rep said doctors diagnosed the singer with exhaustion and she flew home Saturday to her family in Dallas.
Charlize Theron not engaged to Sean Penn 'yet'
Pistorius testifies he didn't consciously pull trigger when he shot girlfriend