Otherbound — Corinne Duyvis

Every time Nolan closes his eyes, he doesn't see darkness. Instead he's transported into the mind of Amara, a girl living in a different world. Nolan's world is our world, full of history tests, family problems and laundry; his parents think he has epilepsy, judging from his frequent blackouts. Amara's world is full of magic and danger and she's a mute slave girl who's tasked with protecting a renegade princess. Nolan is an observer only in Amara's world - until he's not. At first, Amara's terrified by this new presence controlling her. But they eventually learn that the only way to protect the princess and escape danger is to work together.