Article continues below advertisementBritney Spears is facing mounting concern from those closest to her, with insiders telling OK! her recent DUI arrest has intensified calls for her to enter rehab as fears grow over her well-being.Spears, 44, was recently arrested in Newbury Park, Calif., on suspicion of driving under the influence after reports of an erratic driver on the U.S. 101 freeway near the Ventura-Los Angeles county line. She was the sole occupant of a black BMW 430i and underwent field sobriety tests at the scene, while further chemical test results remain pending.