Nightmare king
(Book)

"Things haven't been the same since Shane's accident. One minute he was a normal kid playing a game of tag with his friends, and the next he's the boy who came back from the dead. Now, every time Shane falls asleep, he's pulled into a dark world where the evil Nightmare King reigns. The King is collecting children and keeping them as treasure. Despite the threat of capture by the Nightmare King, he can't stay awake forever. Shane will have to take matters into his own hands . . . if he gives himself over to his nightmares, can he hold on to the good in himself long enough to bring down the King?" --,Publisher's description.