HRV is indeed interesting. I am a lifetime endurance athlete and still train regularly in my 70’s. I started watching my HRV 18 months ago. I was surprised that even when I was feeling good and fit from workouts, my overnight HRV was often low.
An accident kept me from working out for 10 days and my HRV steadily climbed into whatever the “proper zone” is. I now watch it as an indicator of over-training and find it useful.
Same here…could also be whatever is measuring it..,