THE DRIVER (MYSELF) WAS REAR ENDED BY A HONDA CIVIC TRAVELING AT APPROXIMATELY 100 MPH. UPON IMPACT THE BACK OF THE DRIVER'S SEAT FAILED AND PROCEEDED TO CHANGE FROM 90 DEGREES IN SHAPE TO 150 DEGREES IN SHAPE. I THEREBY LOST SIGHT OF THE ROAD AND ONLY HAD THE STEERING WHEEL TO HOLD ON TO. WHEN I APPLIED THE BRAKES I WAS THROWN FORWARD AND EITHER SMACKED THE DRIVER'S SIDE WINDOW, A-POST OR WINDSHIELD WITH MY HEAD.*AK