Gastritis Support Group
Gastritis is a medical term for inflammation of the lining of the stomach. It means that white blood cells move into the wall of the stomach as a response to some type of injury. Gastritis has many underlying causes, from infection with the bacterium H. pylori, bile reflux, or excessive consumption of alcohol or certain foods or drugs like aspirin.

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To my mind, there are three possibilities here (I have no idea what a physician would say to this):
1. there is no connection
2. the gastritis actually preceded the shingles (I just didn't notice it), by perhaps weakening my immune system
3. the shingles caused the gastritis (not sure how this would work), but the shingles did seem to come first
As for the gastritis, after 6 months of bewildering symptoms, it was finally diagnosed through endoscopy two weeks ago. Not sure how they will treat it at this point (am now on a PPI) or if it will ever go away.
I like all of your theories. As with all things if you mention these to the medical world you get a resounding NO CONNECTION. I'll wait and see. I had shingles in 2009 and started getting symptoms of gastritis about 5 months after they had healed. As I fit no normal categories for gastritis I wondered about a connection.
Are you taking any probitoics for your gastritis at all? You need to be careful of PPI as the may relieve the symptoms but won't heal anything. They can also lower stomach acid which won't help matters. If you do go on them be prepared for a rebound effect when you come off them. I was only on them 1 month but others here can tell you about the rebound pain.
Good luck and trawl through the feeds to get all the help you can.