WHILE DRIVING ON THE HIGHWAY I FELT MY HEAD JERK FORWARD AND HEARD A POP FROM MY HEADREST. AT THE TIME I WAS DRIVING STRAIGHT GOING ABOUT 68 MPH. WHEN I FELT THE IMPACT BEHIND MY HEAD MY INSTINCT WAS TO HIT MY BRAKE THINKING SOMEONE HAD HIT ME FROM BEHIND, BUT ONCE I LOOKED AROUND THERE WAS NO ONE CLOSE BEHIND OR TO THE SIDES OF ME. I PULLED OFF THE HIGHWAY AND LOOKED AT THE HEADREST AND NOTICED IT HAD POPPED OPEN. THIS ONLY OCCURRED ON THE DRIVER SEAT HEADREST. AGAIN, I WAS NOT INVOLVED IN ANY COLLISION AT OR AROUND THE TIME OF THE INCIDENT. I HAVE BEEN IN COLLISIONS YEARS PRIOR TO THIS, BUT NONE FROM BEHIND.