Nicola Peate, 25, visited the burger shop Almost Famous in Liverpool after work, bit into an over-sized burger and laughed off the pain, but it became "unbearable" the following day, the British tabloid the Mirror reported Tuesday.
"I didn't think I'd dislocated it. You don't expect it to happen eating a burger. The next morning I woke up and felt really ill. The whole side of my head was hurting," Peate told the Liverpool Echo.
A hospital X-ray indicated a dislocation, and a doctor manipulated the jaw into place, the Mirror said, adding Peate suffers from Ehlers Danlos syndrome, and he hyper-flexible joints are prone to dislocation.
A spokesman for the restaurant said people often joke that the size of its hamburgers is big enough to dislocate a jaw but this was the first case of it actually occurring.