A fluidization level sensor and controller for use in a fluidized patient support surface has a controller coupled to a sensor and a compressor. The patient support surface contains a mass of granular particles housed in frame walls and supported by a diffuser. The compressor forces a fluid, typically air, into a plenum chamber and through the diffuser. The fluid flows through the mass of granular particles, causing the mass of granular particles to fluidize, and exits through a fluid permeable sheet. The fluidization level sensor produces an output signal proportional to the fluidization level of the mass of granular particles, and provides this output signal to the controller. The controller generates a compressor control signal in response to the output of fluidization level sensor, which in turn adjusts the compressor to maintain a substantially constant fluidization level.