Yeah, as far as I know, vagal tone can only be quantified indirectly through heart rate variability. A good vagal tone means the ability to activate the parasympathetic system when necessary, as some of us tend to have our sympathetic system activated all the time from work or social stress.

That said, I must admit I’m not very well-versed in the topic of the vagus nerve. No wonder I haven’t seen you around, but I hope you can recover your health in due time. Thanks for pointing me out to the vaccine long-haul Reddit btw.