Life-saving diagnosis of a rare but familiar condition

Eamon, a 51-year-old gardener, presents to his GP with an acutely painful jaw, which feels tight and difficult to open.
This is causing him distress and he is apprehensive to talk, since opening his jaw causes severe pain.
Swallowing is also uncomfortable and he is having difficulty eating and drinking. This has been progressing over the previous two hours.
There was no obvious trigger and no injury or trauma preceding his symptoms and Eamon has no history of bruxism or temporomandibular joint dysfunction.