A CPR system includes a retention structure to retain the patient's body, and a compression mechanism to perform CPR compressions to the patient's chest. The CPR system further includes a processor to control the compression mechanism, and thus the performance of the CPR compressions. In embodiments, the CPR system compresses at a rate or frequency that is purposely sub-optimal for circulation at least some of the time, and especially when it is detected that the patient has regained consciousness. An advantage can be that the patient may thus faint again, and therefore perceive less of the unpleasant experience of the mechanical chest compressions that the CPR system continues to perform on them as it preserves them alive.