@Jules & I both had first bite syndrome. It wasn’t fun. She is correct that I found keeping my saliva dilute by drinking a lot (80+ oz non-sugary, non-caffeinated fluids/day) helped a lot in reducing my symptoms. Also, as she mentioned, some foods make it worse. I found tart things like citrus & pineapple were the worst for me but also reacted to sweet, spicy & salty. Another thing that helped me early on was putting the food in my mouth & holding it on my tongue for several seconds before starting to chew. Somehow that alerted my salivary glands w/o causing over reaction by the parotid gland from which the pain emanates.
FBS is caused by irritation to the glossopharyngeal nerve (not uncommon during ES surgery) which innervates the parotid gland among other things. It’s an over-reaction by the parotid during the first few bites when starting to eat that causes the FBS pain.
For most people, FBS goes away w/in a few months after surgery, & it does get less intense over time. My surgeon offered to Rx a nerve pain medication which I chose not to accept.