I experienced light-headedness when going to sleep (3 time a day, for 2 hours, and I trained 45 minutes rest too at the time, so quite often). I could have felt something was wrong.

But truly, I had to get a physical check to get my sport license (it's mandatory and free in my country), and I had a new doctor who really checked me, told me about it and to stop intensive efforts, weird sleep patterns and keep doing endurance sport. Sadly I forgot about the last part after a while.

Can't speak for the OP, but I can feel it. It can be disconcerting when trying to fall asleep.

That's how it started for me too. Noticing it when trying to fall asleep. It slowly got worse until I had an ablation procedure done.

Not OP, but this is the sort of thing that should surface from yearly physicals. Ask your doctor to give you an EKG if this is something that you're concerned about.

In some cases, when EKG shows some signs, the cardiologist can prescribe wearing a Holter monitor for a day that records your heart activity. It will show how many beats are abnormal and the overall state.