Sorry forgot. I am a 21 year old male. And have been running almost everyday for 4 years. with weekly breaks every 4 months or so. Haven't ran in 2 months till i get the ok from my doctor. But I have noticed that physical exertion really tires me out. Ran from my front yard to back to get something in house and was kinda winded.
What you describe is exactly what I have been experiencing for over 2 years now. I have been diagnosed with ectopic beats, which they assure me are benign. I wasn't covinced at first but now I have noticed a pattern. Whenever I am nervous, or when I exert myself I get a run of them. Then at night in bed after an episode i get what feels like my heart has stopped completely, and as the feeling as if my body is shutting down. My heart rate dips to about 54, and I have a special watch to monitor it. I get freaked out and sit up bolt ridgid in fear. I have been to A&E on many an ocassion due to being petrified, only to be told it's anxiety. The racing feeling after one of these episodes are an anxiety response, that I do know. All tests including 7 day holter, egc's galore, ultra sound have all came back 'normal' with the exception of Incomplete Right Bundle Branch Block (IRBBB). My cardiologist tells me that this is fine and has probably been there all my life. I did some research and IRBBB symptoms are strikingly similar to what I am experiencing, so I'm not sure she is right. After all it isn't skipping beats for nothing. I also have a small hiatus hernia which can cause all sorts of problems due to the vagus nerve link. Whatever it is that we are experiencing it is most certainly annoying, and the lack of a firm diagnosis is even worse. Hope you get/got sorted out.