I can pretty well guarantee it's not an allergic reaction. No history of allergies to anything, no other symptoms, inflammation is only on the one side, onset has taken hours-not-minutes. What is a "parotid gland" infection?
Let us assume a swollen parotid gland. Sufficiently urgent to find a 24hr facility (there may not be a 24hr urgent care facility anywhere around so this likely means an ER visit)? I dislike abusing ERs as they are dealing with life-and-death issues, so I will do it if this is that sort of emergency but would avoid it otherwise.
I don't know how often you get follow-ups to these sorts of things, but I thought I would let you know the outcome.
As a former emergency medical technician instructor, I evaluated the situation as not needing an ER. It clearly was not an anaphylactic reaction and also did not appear to be an infection. On further research the symptoms were consistent a calculus in the parotid.
I made an appointment with an ENT the following morning but could not be seen until yesterday (Wednesday). By midday Monday the swelling, including in response to eating, had largely subsided, with only a small amount of residual inflammation. By my Wednesday appointment it was almost gone.
The ENT concluded that it was a small calculus that had passed on its own and confirmed that there was no infection. As of today I am completely symptom free.
Thanks for your assessment on Sunday. That particular disorder was one with which I was unfamiliar.