JOIN USSeventeen-year-old Holly Thompson's mouth was stuck open due to the big yawn.
She had to be taken to hospital as she had dislocated her jaw, The Sun reported.
Holly first told her classmate who attempted to shut her mouth, but without success. The school nurse then tried everything from a hot water bottle to ice packs to unlock her jaw, but that didn't help.
She was taken to Northampton General Hospital.
Ejiro Obakponovwe, a doctor, forced 26 wooden splints into her mouth. This enabled it to open enough to tire out the jaw muscles and allowed it to unlock and be put back in place.
"I was so shocked, my expression probably said it all.
"When we realised we couldn't close it, my friend had to tell the teacher. Everyone burst out laughing, it was awful," Holly was quoted as saying.
Holly's footage on YouTube has been seen almost 600,000 times.
She added: "My friends keep asking how my jaw is and saying I'm famous...but I'd rather be famous for something else."