I believe that a Salt deficiency is one of the main causes of our feelings of lethargy; which is often overlooked.
Since takedown; Doctors have always advised I consume more fluids than I’m already drinking.
Salty snacks, appears to makes a difference; although, my Doctor dismisses this.
It would be good if forum members; those who suffer from lethargy/fatigue etc could give my theory a try and report back.