A nerve block should feel about the same as having a tooth numbed or a little less painful. There are a lot of nerves in the mouth that make it more painful. Usually there are two different types of medication in a nerve block, an anesthetic such as lidocaine and a steroid, sometimes they use two different anesthetics.
The reason for using two different ones is that one is short acting, it works right away, the other takes longer to work for may last for days. The steroid will help with inflammation as we all know but it takes days to work. That is why each day you will be feeling something different. As one medication wears off the other will start working. If you get relief immediately, it is a good sigh that the nerve block will work because you are using an anesthetic, it also tell the doc that s/he got the right nerve.
The pain from the injection is actually due to the medication stretching the tissue and the nerves, the slower the medication goes in the less it hurts. The opposite is true of the needle, the faster it goes in the less it hurts.
Shingles can be very painful, and because it is a nerve pain, it is very difficult to treat, Neurontin, Tegretol can be very helpful. I have a posting I am preparing on painful neuropathy that may help. One thing you my want to try is call ZOSTRIX, it is OTC(over the counter), expensive but has helped will all types of pain. The chemical in it is call capisin.
It is the same chemical that causes hot peppers to burn your mouth. It seems strange to use something that will burn but that is how it works. There is a chemical that the body produces called substance P, this sends information to the brain telling it that there is something that is harmful to the body and the brain interprets this as pain. That is what pain is suppose to do. Warn the body about harm. Just like all the other systems in our body we are supposed to have a shut off system, with neuropathy that does not work, we do not know why. There are a lot of things we do not know, too many.
Anyway, the capsin cause the cells to release the substance P, you might wonder why we would want to do that as it would cause more pain. Well, the body can only make so much substance P and in time there is less and less, therefore less pain. At first you will get a burning sensation, this might be too much for shingles pain, over time the pain dissipates. You need to use the medication regularly or else the substance P will build back up. This can be used for arthritis pain as well. If you know anyone who likes to eat hot food, they seem to want it hotter as time goes on, this is the same reason.
Capisin is found in hot peppers, some herbalist will use this, the problem is that the amount of capisin found in peppers not only depends on the pepper type, the soil, climate year so buying the commercially prepared preparation is recommended. There are generic forms OTC but patients seem to like the Zostrix better, the base seems easier to apply. AS ALWAYS CHECK WITH YOUR DOCTOR BEFORE USING ANY THING NEW OR OTC. I hope this is helpful.