VEHICLE WAS PARKED AND BEING LOADED THRU REAR DOOR. I USED CAR REMOTE TO OPEN REAR DOOR AND LOADED ITEMS INTO TRUNK. WITHOUT WARNING REAR DOOR STARTED CLOSING. THIS PROBLEM IS INTERMITTEN AND HAS HAPPENED BEFORE. ON THIS OCCASION DOOR CAME SLAMMING DOWN ON MY HEAD CAUSING A BLOODY INJURY. I HAVE PHOTOS OF MY INJURY. LEXUS HAS BEEN NOTIFIED. THIS PROBLEM IF NOT CORRECTED CAN CAUSE SERIOUS INJURY. THE REAR DOOR COMES DOWN QUICKLY AND IS VERY HEAVY.