Hi. Thanks for your query. Noted the history of having concussion after Novacain injection at the Dentist, nearly passed out, had light headedness and dizziness for weeks - CT scan is normal, EKG normal, not hypoglycemic, got another attack today and felt like passing out; told this to be overactive vagus nerve. Wants to know more... It seems that the fear that increased like a vicious cycle led to the symptoms of light headedness, dizziness and like passing out. Overactive vagus: There is an autonomic nervous system which maintains the homeostasis of the body and mind without us knowing consciously. There are two types. 1. Sympathetic nervous system, which helps for the classical fight or flight mechanism that the person decides. 2. Parasympathetic system run by part of the Vagus nerve and which slows down the heart, increases motility of the gastrointestinal system, reduces the heart so much that the person gets less oxygen and glucose to the brain which is very vital for functioning of the brain and nervous system, wherein falling down is the body s mechanism so that the blood returns to the heart in more quantity so that the heart rate returns back to the normal and the person comes consciousness . Both the systems contradict each other at the same time maintains the balance between the two so that the body functions well. When the vagus tone is increased due to any reason including the fear and so on, the symptoms are the same that you had also called as syncope . I would advise you the following in such a situation: Get the opinion of an Neurologist so that proper clinical evaluation and examination can be done to get the proper management. Get control over your stress and/or anxiety. Proper control of these will help to avoid further attacks.