A system (10) and method for unconscious mask removal detection and adaptive alerting in delivering a flow of gas via a mask (18) to a user's respiratory system comprises an unconscious mask removal detection module (30), a wake-up alert detection module (36), and an adaptive alert module (38). The unconscious mask removal detection module (30) outputs an indication of unconscious removal mask-off or other than removal. The wake-up alert decision module (36) outputs a decision whether to not activate or activate a wake-up alert based on (i) the unconscious mask removal detection module output and (ii) a cost-benefit analysis. The adaptive alert module (38) (i) determines alert settings for the wake-up alert based on (a) behavioral data (58) and (b) historical data (60), and (ii) sends the alert settings to an actuator (28). The actuator (28) actuates the wake-up alert in response to the determined wake-up alert settings to wake-up the user (20) so that the user can put the unconsciously removed mask on again.