This is one of the many grey areas and ambiguities in the Oxford Criteria, oceanblue. For instance, they also state: "psychiatric disorders (including depressive illness, anxiety disorders, and hyperventilation syndrome) are not reasons for exclusion" [emphasis added] Therefore, a participant with fatigue and depression can be included, but a participant with fatigue and low mood / low motivation can, apparently, be excluded. Also of note is the wording of the first question in the operationalised OC: "Is your fatigue (or a synonym), the principal (main, primary) symptom (e.g. tiredness, lack of energy, weariness, exhaustion)?" Fatigue or a synonym. Basically, everyone is welcome except those with demonstrable organic pathology.