1. A pulse oximeter, comprising: a probe that is adapted to be attached to a body part of a patient to create a signal indicative of an oxygen saturation of blood of the patient; and a processor that is adapted to receive the signal produced by the probe, to calculate an SPO2 value based on the signal, to detect a plurality of pattern types of SPO2 indicative of pathophysiologic events, to detect at least one SPO2 shape feature or value of a rise event of one of the pattern types of SPO2, and to recognize a condition of an arousal response failure based on the SPO2 shape feature or the value and produce a warning responsive to said recognizing.