What...

 is ME?
ME is dysfunction of the autonomic nervous system, the sympathetic and stress responses and the immune system. All come at once.
What we need to recreate is the correct responses by all these unconscious physical systems. The root of the nervous system is held in the brain and the spine. From there it reaches out to every part of the body.
In ME the body's stress responses are not working, it is locked in Fight, Flight or Freeze. The parasympathetic responses control the ability to relax and heal. Without this the body cannot recover and learn to live healthily again.
The immune system, again lives in the spine and can be working on overdrive or in complete denial of any foreign bodies. Both these states causes the body physical stress and of course, when the body is ill, the cognitive stress comes along too!