A system configured to detect an awake-to-sleep transition in a subject, the system comprising: a pressure generator configured to generate a pressurized flow of breathable gas for delivery to the airway of the subject; a sensor configured to generate output signals conveying information related to a gas parameter at or near the airway of the subject; a processor configured to execute computer program modules, the computer program modules comprising: a control module configured to control the pressure generator such that the pressure generator adjusts a parameter of the gas in the pressurized flow of breathable gas in order to provide breathing cues to the subject; characterized in that the processor further comprises: a conformance module configured to determine conformance of respiration of the subject to the breathing cues provided by the pressurized flow of breathable gas, wherein the conformance module is configured to determine said conformance by comparing the breathing cues provided by the pressurized flow of breathable gas to one or more breathing parameters that are determined by a breathing parameter module based on the output signals generated by the sensor; and a sleep module configured determine whether the subject is awake or asleep, such determination being based on the determination of conformance made by the conformance module. a pressure generator configured to generate a pressurized flow of breathable gas for delivery to the airway of the subject; a sensor configured to generate output signals conveying information related to a gas parameter at or near the airway of the subject; a processor configured to execute computer program modules, the computer program modules comprising: a control module configured to control the pressure generator such that the pressure generator adjusts a parameter of the gas in the pressurized flow of breathable gas in order to provide breathing cues to the subject; a control module configured to control the pressure generator such that the pressure generator adjusts a parameter of the gas in the pressurized flow of breathable gas in order to provide breathing cues to the subject; characterized in that the processor further comprises: a conformance module configured to determine conformance of respiration of the subject to the breathing cues provided by the pressurized flow of breathable gas, wherein the conformance module is configured to determine said conformance by comparing the breathing cues provided by the pressurized flow of breathable gas to one or more breathing parameters that are determined by a breathing parameter module based on the output signals generated by the sensor; and a sleep module configured determine whether the subject is awake or asleep, such determination being based on the determination of conformance made by the conformance module. a conformance module configured to determine conformance of respiration of the subject to the breathing cues provided by the pressurized flow of breathable gas, wherein the conformance module is configured to determine said conformance by comparing the breathing cues provided by the pressurized flow of breathable gas to one or more breathing parameters that are determined by a breathing parameter module based on the output signals generated by the sensor; and a sleep module configured determine whether the subject is awake or asleep, such determination being based on the determination of conformance made by the conformance module.