Ultimately traceable to neural glucose deprivation, symptoms of hypoglycemia include neurogenic (autonomic) and neuroglycopenic symptoms. Neurogenic symptoms (tremulousness, palpitations, anxiety, sweating, hunger, paresthesias) are the results of the perception of physiologic changes caused by the autonomic nervous system's response to hypoglycemia. Neuroglycopenic symptoms (confusion, sensation of warmth, weakness or fatigue, severe cognitive failure, seizure, coma) are the results of brain glucose deprivation itself. Glycemic thresholds for symptoms of hypoglycemia shift to lower plasma glucose concentrations following recent episodes of hypoglycemia, leading to the syndrome of hypoglycemia unawareness--loss of the warning symptoms of developing hypoglycemia. Thus, patients with recurrent hypoglycemia (e.g., those with tightly controlled diabetes or with an insulinoma) often tolerate abnormally low plasma glucose concentrations without symptoms.