Dream Master Series by Theresa Breslin

Cy is about to wake up from a terrific dream about the Ancient Egypt, but finds that he can re-enter his dream world. But the Dream Master isn't used to boys who want to break all the rules. Cy moves back and forth in time and finds that dream life and real life become ingeniously intertwined. Tied in with National Curriculum.

"We're in trouble again," said the Dream Master. "Twenty Types of Trouble - Double Mixed!"Every dream needs a master - someone in charge, just like someone telling a story. But when Cy has a go at running his own dream, everything goes horribly wrong. Suddenly Viking invaders are burning down a village, chasing after him with huge axes - and a bossy Saxon princess thinks he is a useless swineherd. His dreams are out of control!