A self-leveling bed support frame provides an automatically-controlled level sleeping surface in the sleeper cab of a semi-trailer rig. The self-leveling bed support frame is comprised first of a rectangular lower frame with four pneumatic actuators in each corner. A rectangular upper frame is above the lower frame and engages at its corners with the pneumatic actuators. An automatic control system operates the four pneumatic actuators to maintain a level upper frame by utilizing two pair of mercury switches disposed on two independent control axes. Each pair of mercury switches control the positioning of a pair of the pneumatic actuators, disposed at either end of a diagonal across the upper frame. An adjustable seat back assembly is also provided which can elevate one end of a mattress on the upper frame, using a pair of scissor jack mechanisms, which provide fine control when utilized with a pneumatically controlled actuator.