Probably one of the most-used words in Hollywood -- aside from "scandal" -- is "rehab." It seems nearly every celebrity has sought treatment at one point or another, although the reasons it's needed can vary from mental health to simply "undisclosed." Selena Gomez falls into the latter camp, as her rep has confirmed that the 21-year-old voluntarily packed up for a two-week stay at an Arizona-based rehab center in January. The rep won't say what she needed treatment for, just that it didn't have anything to do with drugs or alcohol. If you're having a hard time buying that, remember scenarios like Gomez's aren't uncommon.