The occurrence of an arousal in a patient associated with an apneic or hypopneic episode can be determined. Sensors are placed on a patient to obtain signals representative of at least two physiological variables, for example skin conductance, heart rate, and blood oxygen concentration. The signals are conditioned by conditioning circuitry, then processed by a processor to correlate at least two thereof. A coincident change in at least two of the processed signals is indicative of the occurrence of an arousal, that in turn indicates an apneic or hypopneic episode has occurred. A patient thus can be diagnosed as suffering conditions such as obstructive sleep apnea.