Apparatus, systems, and methods are provided for treating obstructive sleep apnea. A unitary valve assembly removably located inside the exterior profile of a nasal pillow mask uses positive airway pressure from a low-flow hose to automatically create an on-demand therapeutic air splint in the pharynx. During inspiration the mask's valving system allows room air to be inspired. During exhalation another valve governs therapeutic backpressure equal to the prescribed pressure setting of the CPAP blower machine. The mask may be worn when the CPAP blower machine is off, and systems are provided for turning the CPAP blower machine on only when needed.