IT IS undoubtedly very attractive and satisfying to believe in one plausible and "scientific" biological explanation for feelings of fatigue, weakness, dizzy spells, and exhaustion. This set of symptoms is such a common affliction of mankind that it begs for an explanation in terms of an easily understood chemical change in the body. The modern concept is to blame it all on low blood sugar levels. There is no doubt that periods of true low blood sugar concentrations (hypoglycemia) may produce such symptoms, and, in those cases, raising the blood sugar level back to normal relieves the individual.
Hypoglycemia means, literally, less sugar in the blood. Thus, it is a laboratory finding, not a disorder. However, soon after insulin came into therapeutic use (about 1924), it was found that a "low" blood sugar concentration causes a characteristic train of symptoms: anxiety, tremor, perspiration, dizziness, palpitations, confusion, lethargy, and ultimately loss
Levine R. Hypoglycemia. JAMA. 1974;230(3):462-463. doi:10.1001/jama.1974.03240030074038