While other tissues in the body can use nutrients other than glucose as fuel, the brain cannot. When the level of glucose in the blood drops, brain function is impaired and an anxiety reaction occurs immediately. The adrenaline released by the sympathetic nervous system in response to the brain’s alarm reaction causes glycogen in the liver to break down into glucose, fairly rapidly restoring the blood glucose level to normal. This glycogen-breakdown mechanism takes about twenty to thirty minutes.
Patients suffering from diabetes mellitus, who are being treated with daily injections of insulin, will sometimes experience low blood glucose, or hypoglycemia. The first warning of hypoglycemia is a sudden onset of severe anxiety, and sometimes patients will suddenly develop a gross tremor.
Hypoglycemia can occur also in other conditions, notably functional hypoglycemia. The patient with this disorder is usually either significantly over or significantly under the desirable body weight for height and has probably been consuming a diet consisting of more sugar and refined carbohydrates than is recommended by nutritionists. It is found in this disorder that the fasting blood glucose level will be normal, but at a particular time interval following a carbohydrate meal, the blood glucose drops below the fasting level. At that time, the nervous system will become inefficient and trigger off an anxiety reaction. It is obvious that a person with functional hypoglycemia will experience stress breakdown symptoms under a lesser level of stress than would be expected, when the blood glucose level drops.