WHILE DRIVING APPROXIMATELY 58 MPH IN RAINY WEATHER WITH A TRAILER ATTACHED, TRAILER STARTED TO FISHTAIL WHILE GOING DOWN HILL. TRAILER HAD SWUNG AROUND AND BROKE FREE OF THE HITCH AND HIT THE SIDE OF TRUCK. TRUCK GRAZED AN ENBANKMENT, AND WENT INTO THE MEDIUM STRIP, HITTING ANOTHER VEHICLE HEAD ON. VEHICLE WAS TOTALED, AND DRIVER SUFFERED A HEAD INJURY AND FRACTURED VERTEBRATE. NEITHER AIR BAG DEPLOYED UPON THE FRONTAL IMPACT. PLEASE DESCRIBE DETAILS. *AK