Request #369 From Ladd

I read this book when I was very young, and I remember little about it. I am not even 100% sure that it even is a YA book.  It is a horror book about a boy who slowly realizes that he is experiencing a demonic possession. One of the first things he notices is that his feet are filthy and there is dirt and leaves in his bed when he wakes up. He realizes he’s been outside at night for hours, presumably sleepwalking.  He somehow gets some help from a priest, who gives him a cross chain that has been blessed or something, which staves off his demon for a time. He has a friend who I think keeps an eye on him to see if he “relapses”. One day, the chain begins really irritating his skin so he removes it, and shortly after collapses to the ground. I distinctly remember the text describing how the friend opens his mouth to “make sure he hasn’t swallowed his tongue”.  I also remember this one weird line of text. The priest (I think) asks him a question. Something along the lines of “why don’t you like me?” / “why do you hate me?” / “why are you displaying aggression or disdain towards me?” The possessed boy responds: “Because you’re a [“x” almost sure it was a name].” And [X’s] are the enemy.”  The word “enemy” was in italics exactly that way, if that helps. I wish I had more to give you! I know this is so random and disjointed, but I don’t remember anything else about the book other than the fact that it scared the daylights out of me when I was a kid. I’d be supremely impressed if anyone solved this.