Jackson suffered from hypoglycemia a condition in which the level of glucose in the blood is very low. The chief symptom is fatigue and lack of endurance, since the condition essentially starves the cells, particularly the energy-hungry muscle cells. Normally, higher levels of blood glucose, such as following a meal, trigger insulin release, which then signals cells to extract the glucose from the blood. (Cells that do not require as much glucose as they are triggered to receive store the excess as glycogen, a starch-like compound, or as fat.) In Jackson's particular case, a adenoma in his pancreas produced too much insulin all the time, keeping his blood sugar level too low. Removal of the growth corrected the problem. There are also cases of hypoglycemia with no identifiable cause, and it is an occasional complication of diabetes, usually caused by an incorrect dosage of injectable insulin.