Effect of nerve pills and relationship to Shingles
I gather you are talking about anti-axiety drugs (anxiolytics). Benzodiazepines is one of the major groups of anxiolytics, and includes Xanax. Benzodiazepines are central nervous depressants, meaning that they reduce the activity of neurotransmitters in the brain. They do this by binding to the GABA-A receptor and enhancing the effect of the inhibitory neurotransmitter GABA when it binds to the same receptor. The binding of GABA to a GABA receptor on a neuron causes hyperpolarization of the neuron by ion flow through the cellular membrane and decreases the chance of an action potential. So yes, nerve pills act by supressing the nervous system.

As for your question about interaction with Shingles, I think that's considered off-topic under the personal medical questions policy.