VEHICLE WAS REAR ENDED WHILE AT A COMPLETE STOP. UPON IMPACT, BOTH FRONT SEAT BACKS SNAPPED AND COLLAPSED BACKWARDS, CAUSING THE DRIVER TO FALL BACKWARDS;HIS FOOT SLIPPING OFF THE BRAKE PEDAL. VEHICLE CAREENED ACROSS THE STREET ONTO A FIELD 150 FOOT AWAY. DRIVER WAS NOT INJURED. HOWEVER, THE PASSENGER WAS TAKEN TO THE HOSPITAL FOR EMERGENCY TREATMENT.*AK