Some researchers think ME/CFS is like PTSD but it's internal; instead of over-reacting to outside events such as doors slamming ME/CFS patients are over-reacting to internal physiological events. Their brain's are interpreting normal events as dangerous and thus raising the fear response as you mentioned.
It's interesting that that is in a way Dr. Light's thesis and he has some evidence for it; i.e. his findings that the sensory receptors for muscle damage on our white blood cells are over-reacting to normal amounts of lactic acid, ATP, etc. Ih his view its not the brain though but sensory receptors in our body.
This neural retraining is an interesting idea. I've tried to express it elsewhere since as the neurology starts healing with the active b12 protocol the brain appears to be much more plastic and open to retraining while repairing the myelin and growing neurons. It's a tumultuous period when that is happening and people who are fearful train themselves in nonopportune patterns. The brain is not restored to it's former state merely by healing since much of that previous state is shaped by training. It's very much like being a new person and having the opportunity to reshape ourselves.