Thanks for your question and concern as there are many diseases herp zoster is also a disease which Is caused by same virus that in result cause a disease like chicken pox.It disturb the body and it affect the nerve of one side of trunk.Today doctor have noticed that vitamin b12 relieves the symptoms of postherpetic neuralgia.There are different vitamins and according to vitamin b complex are absolutely essential for the necessary metabolic process such as rbc cell,which help to keep nervous system and energy production maintain.Vitamin b provide carbohydrate and convert them to glucose as all vitamin b are complex.For the metabolism and fat vitamin b complex are very rssential.While taking vitamin b it is really important to take them all at the same time.Lossing weight and vitamin b losses up and down only if taken together. Riboflavin(B2), Niacin(B3), Panthotenic Acid(B5),Pyridoxine (B6), Cyanocobalamin (B12). Vitamin b 12 helps in many ways like it increses in weight loss ,helps in fighting with stress and depression.As it also result in anemia and anxiety.If we alk about overdose it is rare in case people take because it is a water soluble vitamin and the vitamin b taken is eleminated by urine.As a result you can have negative effect as rash or allergy in your body but the possibilty of dents in the nail are not there. So I would suggest you to consult your doctor again.Take care.