Bullet in the head without you knowing it?

There's an article in the news lately citing that a Polish man found a bullet at the back of his head. Problem is, he didn't know it. How is that possible? Seems very much possible for this guy as he said he was too drunk to know what happened back then. The incident happened back in new year's eve of 2005. The only thing he could slightly remembered was that he felt a big knock at the back of his head. Now, this is what I call the power of alcohol.

After 5 years, the bullet was removed. He thought that was just a simple removal of a cyst at the back of his head!!

Wonder if he ever got brain damage!
Bravo...