The remainder is in the blood stream and other organs.
Potassium is primarily an intra cellular ion.
A number of medical conditions that cause low potassium are associated with fatigue. Eight pairs subjects in this study had a whole body DEXA scan which showed no significant difference in the amount of lean body mass or total bone mass. Patents with CFS were divided into two groups, those with fatigue symptoms only and those patients who had a mixed symptomatology of fatigue and myalgia. This was defined by patient assessment of their disability at the medical consultation. The serum potassium levels were normal in all subjects.