Aside from a personal anecdote, I don't really have much to offer. I know that when I get anxious I swallow a lot. Its called aerophagea, basically the dry swallowing of air.
Since your testing came back all normal this is a possibility.
Dairy and raw vegetables and beans will all cause excess gas. Have you added anything new to your diet lately? even medications or supplements?
Thoracic Outlet Syndrome, Migraines, Anxiety, PCOS