'The Walking Dead' Stuntman Hospitalized After Falling 20 Feet On Set

A 'Walking Dead' stuntman fell more than 20 feet onto a concrete floor ... suffering a serious head injury that sent him to the hospital.

John Bernecker was reportedly on set Wednesday in Georgia when the accident happened. It's unclear how he fell or if he was in the middle of shooting a scene -- but he had to be airlifted to Atlanta Medical Center where he's in ICU.

His girlfriend posted a Facebook message, saying ... "John deserves to be seen by every neorusurgeon and doctor there is until one of them sees the life we all know he has in him and bring him back to us... THIS ISNT FAIR."

John -- who specializes in high falls -- has also worked on "24: Legacy" and 'The Hunger Games: Mockingjay.'