As of 2015, Mayo Clinic and Cleveland Clinic both offer evidence-based lists of low blood sugar symptoms, according to their websites. Symptoms of low blood sugar, or hypoglycemia, include heart palpitations, pale skin, fatigue, irritability and shakiness.
Hypoglycemia occurs when the level of sugar in the blood is below 70 milligrams per deciliter, explains Cleveland Clinic. If hypoglycemia worsens, some patients experience more serious symptoms, such as seizures, blurred vision, confusion, abnormal behavior and loss of consciousness, as stated by Mayo Clinic.
Low blood sugar can be caused by skipping meals, not eating enough carbohydrates, drinking alcohol on an empty stomach, or a higher than normal activity level, according to Cleveland Clinic.