Anyone experimented with Heart Rate Variability measurement?

If the theory about CFS being caused by an infection of the vagus nerve leading to chronic activation of the sympathetic nervous system is correct, then it should show up in Heart Rate Variability measurements. HRV is supposed to correlate with parasympathetic nervous system arousal. I saw a psychologist a few years ago who was right into it when I was really stressed out and this technology first hit the market, but the devices at the time were specialized and expensive and I never asked him to test me, so I never actually got my HRV measured.

Now HRV measurement devices are relatively cheap though, and a friend of mine recently put me onto the EliteHRV app, which works on an iPhone with a relatively inexpensive Polar H7 Heart Rate Sensor.

The basic idea is that the more time your body spends in parasympathetic arousal, associated with higher HRV readings, the more recovery/healing you get.

I’ve just started this morning with my first Morning Readiness reading; so it’s too early to give any concrete results. I have noticed that my HRV drops while playing Yousician Piano, presumably because I’m still learning and the challenge of getting the notes right is mildly stressful. I hope this changes as I play better, since I play music to relax; not to get more stressed.

Anyone else experimented with HRV measuments?