Techniques are provided for detecting atrial events that might be hidden due to the operation of a post-ventricular atrial blanking (PVAB) interval or other atrial channel blanking interval. In one example, candidate atrial events are identified within signals occurring during the PVAB interval. Then, a determination is made as to whether the candidate atrial event is a true atrial event based on a comparison of characteristics of the candidate atrial event with characteristics of prior known atrial events within the patient. By comparing the characteristics of the “hidden” event with the characteristics of prior known atrial events within the patient, a quick and accurate determination can be made whether the event should be counted as a P-wave. In this manner, hidden atrial arrhythmias can be detected and mode switch oscillations can be reduced or eliminated.