Na, this was real. I have lots of experience with bogus HR readings, especially on my Polar.

I suspect the drop is easily repeatable, though I was hoping others had experience with it. ~10 years ago I did do a stress test as a part of a comprehensive physical (there wasn't any reason to do it otherwise), and I remember the cardiologist did note there was something [an arrhythmia I assume], but said it was not uncommon and not to be concerned about. I'll get this checked out though.