A device for treating sleep apnea by discriminating between successive sleep stages of a patient includes a generator configured to produce stimulation pulses, a stimulator that receives the stimulation pulses produced by the generator and delivers stimulation to the patient, a sensor configured to measure a biological parameter of the patient, and a controller. The controller is configured to determine a state of the patient based on the biological parameter, perform a sleep analysis based on the state of the patient, activate the generator to trigger production of the stimulation pulses, determine a variation of the biological parameter subsequent to the production of the stimulation pulses, determine a response of the patient to the stimulation pulses according to the variation of the biological parameter, and determine a sleep stage of the patient based on the response.