While driving home from the gym with my daughter in the front passenger seat, we were traveling less than 40 mph under normal driving conditions. Without warning, I heard a very loud pop/bang from inside the vehicle. We had not been in a collision, had not hit anything, and nothing had struck the vehicle. I immediately looked over and saw my daughter crouched down in her seat holding her neck. At first, I could not determine what had happened. I then noticed that the front passenger-side Active Head Restraint (AHR)/headrest had suddenly deployed or come apart and had struck her from behind. There were no warning lights, messages, alerts, or other symptoms before the incident. The deployment occurred suddenly and without any apparent event that should have triggered this safety system. My daughter sustained a neck injury as a result of the unexpected deployment and was taken to the hospital for evaluation and treatment. She was placed in a neck brace and had to wear it for approximately one week. The incident also created a safety risk while the vehicle was in motion. The sudden loud bang and my daughter's immediate reaction occurred without warning while I was driving, and I initially did not know whether something had struck the vehicle or what had happened to her. The vehicle has not yet been inspected by a dealer, manufacturer, insurance representative, police, or independent service center. The passenger-side Active Head Restraint remains in its deployed/dislodged con