I was traveling on highway going posted speed of 70mph. There were no cars anywhere close to front of vehicle. Car automatically braked HARD, locking the seatbelt and throwing everything in car forward. It was not a "warning" brake it was a ridiculously HARD brake to attempt to stop car. I am shocked and amazed it did not cause accident or flip. As a result of this sudden hard stop, I have having back and neck pain as well as chest and shoulder pain. There was no reason for this to occur, there was nothing in front of the vehicle at all. There were however cars behind that nearly hit me. I may seek medical if back, neck and shoulder continue to hurt.