Who doesn't meditate and why?

[Navaratna]

That is the parasympathetic system.

In my early days of meditating I was focused a lot on making the parasympathetic system conscious and gaining awareness of the automatic body functions.
At this point, if I'm not consciously breathing I unintentionally end up holding my breath and sometimes it is only shortness of breath that reminds me to keep up my rhythm. Especially if my mind is solely focused on something else. Breathing is, in my experience, the most effective way to get in to deep meditation.

Slowing your heartbeat is something used in some martial arts as well.

I'm familiar with the autonomic and parasympathetic systems.

It's described in Sahaja meditation in Shri Mataji's speeches.

I thought this was interesting. Buddhist monks were scanned and they discovered both nerve systems were activated at once during their meditations. It hadn't been discovered before.

https://www.bbc.com/news/world-us-canada-12661646