Isidro Mejia was working on the roof of a new house under construction in Antelope Valley in Los Angeles County, California.

Mejia stumbled on scaffolding and toppled on top of a fellow worker on the floor below. The worker on the second floor was framing with two-by-fours — using a pneumatic nail gun.

Witnesses told authorities that when Mejia’s falling body struck the worker on the second floor, the worker "tensed up to keep his balance." He grabbed a two-by-four with one hand, but he also increased his grip on the nail gun’s trigger, causing the gun to fire its 3 1/2 inch nails continuously, according to news reports from the Los Angeles Times.

How serious were Mejia’s injuries?

He arrived at the ER in a helicopter with six 3-˝ inch nails stuck in his head — including three in his brain and one in his spinal column.

One nail punctured the skull and was at the midline of the brain, an area filled with blood vessels. A second nail penetrated to within two millimeters of the brainstem, an area that controls all movement and breathing.

A third nail penetrated the spinal column but did not hit the spinal cord itself. Otherwise, Mejia would have become an instant quadriplegic, rendering him unable to move or breathe.

Now what?

A neurosurgeon at Providence Holy Cross Medical Center in Mission Hills said "medical textbooks cover bullets and metal fragments from car wrecks, but there’s no information about removing nails from the brain."

The surgeon began — ever so slowly — removing the long nails, one by one. Four days after the nails punctured Mejia’s skull, the last nail was removed. Days later the swelling in the brain went down.

Mejia was conscious. He spoke only in Spanish because he had lost all memory of his English speaking skills. The injured construction worker, through his wife, thanked the doctor who had saved him, and added: "I feel lucky...I know I’m lucky because I’m alive."