I don't think you should be afraid. He's just trying to tell you something. Maybe you should read that book, it might reveal what that lamb thing ment. If it doesn't go back to his house and try to find something that will. I know that probably sounds stupid and you probably already tried it but I think if you find the meaning of that symbol and the lamb thing, then maybe those nightmares will go away. Maybe your dreams are connected somehow, I mean other than the fact that they are freaky.