An implantable cardiac stimulation device is described wherein a controller of the cardiac stimulation device controls selected functions of the device based on whether the patient is at rest and further based on whether the patient is prone to vagally-mediated arrhythmias. Functions of the device that may be controlled include, for example, a pacing base rate, an AV/PV delay, and a refractory period as well as overdrive pacing parameters and diagnostic data gathering parameters. In one example, if the patient is not prone to vagally-mediated arrhythmias, the base rate is lowered while the patient is at rest. Also, overdrive pacing parameters are set to be less aggressive. As such, the operation of the cardiac stimulation device is controlled to make it easier for the patient to rest while also reducing power consumption. However, if the patient is prone to vagally-mediated arrhythmias, the base rate is not lowered while the patient is at rest. Overdrive pacing parameters are instead set to be more aggressive, rather than less aggressive. In this manner, the cardiac stimulation device attempts to compensate for any increased risk of arrhythmia that may occur while the patient, who is prone to vagally-mediated arrhythmias, is at rest. Numerous other parameters may be adjusted dependent upon whether the patient is at rest or dependent upon whether the patient is prone to vagally-mediated arrhythmias.