Thanks for advice, Ian. I did get it checked out (24-hr and 7-day monitors, Electro- and Echocardiograms, consultations with heart specialists) but no action was required as the symptoms subsided each time within the timeframe required for the tests and consultations.

I forgot to mention the strange restless, breathless feelings I used to get as well, where I felt the need to keep taking deep breaths but they never satisfied me, while at the same time being physically rocked by my heart banging away in my chest, with frequent stops and multiple beats thrown in. It was the only time I was physically aware of my heart beating while at rest. That was a few years ago now, thank goodness.