I was out running a few weeks back, nothing crazy, just to blow off some steam. Afterwards felt some weird discomfort/palpitations and checked my heart rate. Heart was "skipping" beats if that makes any sense. This continued for hours and eventually I went to the ER. They monitored me, blood tests, etc... and they did see the "skipping" but said it was actually my heart beating an extra beat, which threw off the rhythm. They scheduled me for follow up tests but said this is pretty common and given all my other tests were fine, it's probably nothing to worry about. But honestly, I haven't been able to work up the courage to run again, it just freaked me out too much. I have been doing brisk walks for 1 hour each day instead, by the end I actually have worked up a bit of a sweat (around 7.5-8km or so) and it's going ok. But just way too freaked out until I see the doctor again to try running. I do a lot of heart rate training and I have never noticed this happening before, so it's definitely weird to me.