FREEWAY DRIVING AT SPEED LIMIT (65MPH) PASSENGER SEAT HEAD REST SELF ENERGIZED CAUSING PASSENGER TO BECOME UNCONCIOUS FOR ONE OR TWO MINUTES, WITHOUT WARNING. AUTO HAD NO ACCICENTS NOR ANY OTHER DAMAGE TO HEADREST OR SEAT. PASSENGER COMMENT AFTER HE BECAME CONCIOUS WAS "WHY DID YOU HIT ME." PRECEEDED BY A NOISE LIKE A METAL PIPE BEING DROPPED. THERE WAS NO REASON FOR THE 'REAR END COLLISION SENSOR LOCATED AT SEAT BASE TO ENERGIZE. THE HEADREST CAME FORWARD STRIKING BACK OF HEAD CAUSING A POSSIBLE CONCUSION. A DIFFERENT RESULT WOULD HAVE CAUSED DEATH IF IT WAS THE DRIVER SIDE. FAILURE WAS CAUSED BE SPRING TENSION CONTINIOUS ON PLASTIC AND BOTH THE FRONT AND REAR PIECES, BUT ONLY THE FRONT PART IS AVAILABLE FOR REPAIR. THIS FORCES REPLACEMENT OF THE ENTIRE HEADREST ASSEMBLY. (QUOTED $792). REPAIR NOT AVAILABLE IN A TIMELY MANNER.