I PARKED MY CAR PARALLEL TO THE CURB ON A CITY STREET. I MOVED THE SHIFTER FROM "DRIVE" TO "PARK". I DID NOT TURN OFF THE ENGINE BECAUSE I WAS ONLY GOING TO GET OUT FOR A FEW SECONDS TO OPEN THE DOOR BEHIND ME TO LET SOME SENIOR CITIZENS TO GET IN THE CAR. I RELEASED MY SEAT BELT BUCKLE AND PROCEED TO OPEN THE DRIVER-SIDE CAR DOOR. AS SOON AS MY FEET WERE ON THE GROUND AND MY BODY WAS OUTSIDE OF THE CAR, THE CAR STARTED TO MOVE IN REVERSE DIRECTION. THE CAR WAS MOVING FAIRLY QUICKLY BECAUSE WITHIN A SPLIT SECOND, I WAS KNOCKED TO THE GROUND BY THE CAR DOOR WITH THE LEFT FRONT WHEEL ON TOP OF MY LEFT FOOT. THE WHEEL PROCEEDED TO ROLL OVER MY LEFT ANKLE, LEG, THIGH, HIP, ABDOMEN, CHEST, AND FINALLY MY RIGHT UPPER ARM AND SHOULDER JOINT. THE CAR CONTINUED TO TRAVEL IN REVERSE BY JUMPING THE CURB ONTO THE SIDE WALK AND FINALLY STOPPED BY HEAVY BUSHES IN FRONT OF A BUILDING. UPON INSPECTION, THE SHIFTER HAD SLIPPED INTO THE "REVERSE" POSITION. BASED ON THE GRADIENT OF THE ROAD SERVICE WITH THE ENGINE RUNNING, THE REMOVAL OF MY FOOT ON THE BRAKE WOULD HAVE IMMEDIATELY ALLOWED THE CAR TO MOVE BACKWARD HAD THE SHIFTER WAS IN REVERSE WHICH WOULD MAKE EXITING MY WHOLE BODY OUT OF THE CAR WITHOUT NOTICING CAR MOVEMENT VERY UNLIKELY IF NOT IMPOSSIBLE, PARTICULARLY FOR A 72 YEAR OLD MALE WHO IS RECOVERING FROM AN OPEN HEART SURGERY AND TWO BRAIN SURGERIES. THE SHIFTING MECHANISM AND THE ASSOCIATED CONTROL MUST BE FAULTY RESULTING IN THE "FALSE PARK" POSITION.