Overactive vagus nerve disorders can be triggered by a number of different causes. The vagus nerve diverts blood to the stomach and may divert too much away from the brain when a patient is vomiting, digesting a large meal, or having a bowel movement.agus nerve disorders that are this severe are rare and often either congenital or the result of a serious illness or injury to the nerve. Patients may also suffer from vagus nerve issues that are caused by an overactive vagus nerve. The main symptom of these disorders is fainting.