Once a friend of mine had a dream where he knew that his heart has stopped. He was feeling calm yet little edgy because he 'was aware' of the situation. He told me that he could feel/know or hear that someone "said" it wasnt his time to go yet, so he would hit himself in the chest few times and say 'lets just jumpstart the heart again' while feeling super calm or 'normal/natural', and he woke up with a pain in his chest, right above his heart where he hit himself in that dream. He was sleeping with a sport watch on his wrist, which he had forgotten to take off, he checked the info about his heartrate the same day and was little shooked, because it showed that his heartbeat had gone waayyyy too low during that night, around 30bpm.. so he didn't know about it until he "woke up" in that dream-like state.