Dr. Flagg grew up in Nashville Tennessee. He served as a Battalion Flight Surgeon and Brigade Flight Surgeon during his combat tour in Iraq with the United States Army, Combat Aviation Brigade, 1st Cavalry Division. Following his combat tour, he was promoted to the rank of Major and appointed as the Chief Flight Surgeon and Chief of the Physical Exam Section at the DiLorenzo TRICARE Health Clinic at the Pentagon.

He completed his residency in Anesthesiology and further enhance his medical training with a Fellowship in Pain Medicine, both at the Johns Hopkins University School of Medicine. During his training, he received the Clinical Anesthesia (One) resident of the year award for outstanding achievement in patient care and citizenship. He subsequently was selected as Chief Resident for the 2011-2012 Academic Year.