2006 LEXUS LS Electrical System Problems

I OWN A 2006 LEXUS LS430, WHICH I'VE HAD SINCE NEW. IT ONLY HAS ABOUT 70K MILES ON IT AND HAS BEEN MAINTAINED SOLELY AT LEXUS DEALERSHIP WHERE VEHICLE WAS PURCHASED IN RALEIGH NC. TODAY WHILE REVERSING DOWN A STEEP DRIVE MY VEHICLE SUDDENLY LOST POWER AND CUT OFF. I LOST ALL HYDRAULIC BRAKE ASSISTANCE AND STEERING ASSIST. I WAS MOVING AT ABOUT 8 MPH AT TIME OF FAILURE. NO MALFUNCTION INDICATORS APPEARED ON THE DASH BEFORE OR AFTER THIS. MY VEHICLE HAD AT LEAST 10 GALLONS OF FUEL IN THE TANK AS IT INDICATES ABOUT ⅝ FULL. I WAS ABLE TO RESTART THE VEHICLE AFTER STOPPING AND THE CAR RAN FINE ON MY WAY HOME. I AM SCHEDULING AN APPOINTMENT WITH DEALERSHIP FOR INSPECTION BUT THIS WAS SCARY AND I'M JUST CONCERNED IF THE SAME THING HAPPENED AT HIGHWAY SPEEDS IF IT COULD BE FATAL LIKE THE GM IGNITION...