False fatigue alarms / functional disorder

This is the idea that, after a prolonged trigger, the nervous system can get 'stuck' over-predicting threat and generating fatigue, effort, and other symptoms disproportionate to any peripheral damage — a predictive-coding or functional-disorder framing. It is the only mechanism with no confirmatory test: it is reached by ruling other things out, and its likelihood rises as organic mechanisms are excluded. This is real and treatable, and it coexists with organic drivers rather than replacing them — it is never 'all in your head.' Pacing, CBT (which helps coping and fatigue but does not assume a psychological cause), and acceptance-based approaches can help; heavily-marketed brain-retraining programs (DNRS, Lightning Process, Gupta) have weak, conflicted evidence and can do harm by implying non-recovery is the patient's fault.