This very thorough and clearly written article discusses the the title of this thread. Interestingly, I learned the autonomic nervous system is comprised of three parts: the sympathetic (flight/fight), parasympathetic (rest/digest), and enteric (digestive) systems -- I didn't know about the last one -- I thought it was subsumed under the parasympathetic system!

https://thedysautonomiaproject.org/g...-there-a-link/

The site puts out a book I just ordered -- written page by page for doctors and patients. It has great reviews.