I was driving in the vehicle to put gas in, all of the sudden, i heard something snap and felt something hit the back of my head really hard. I felt disoriented as I didn't know what had happened. When I stopped and look at the seat, I noticed that head rest had deployed suddenly without warning and hit the back of my head. There was no accident that should have caused the head rest deployment. I sat there disoriented and started getting a headache and my neck started getting stiff. It's been a week since it happened, if it doesn't go away , I will be seeing a doctor as the pain comes and goes.