We all have a pot of energy which is available to us to spend over the day. What prevents us spending too much is the symptom of fatigue.
We have to spend that pot of energy just to stay alive in “house keeping” duties – but in addition mentally, physically, emotionally or immunologically.
In ME/CFS either that pot of energy can be small (because of poor mitochondrial function, poor fuel supply, poor adrenal function, poor thyroid function and so on), or we can be spending energy wastefully.
Of course, the business of pacing is all about spending mental and physical energy judiciously. Many have experienced how energy sapping it is to expend emotional energy.