What Is It? Hypoglycemia is an abnormally low level of blood sugar (blood glucose). Because the brain depends on blood sugar as its primary source of energy, hypoglycemia interferes with the brainís ability to function properly. This can cause dizziness, headache, blurred vision, difficulty concentrating and other neurological symptoms. Hypoglycemia also triggers the release of body hormones, such as epinephrine and norepinephrine. Your brain relies on these hormones to raise blood sugar levels.