Inside the book

I dreamed I was reading a very interesting book. The action was happening in the medival times, in forests and mountains. If I concentrated hard enough, I could get inside this book, get into the story and become part of it. The only problem was that it was hard to go back to the real world, it could even happen that there won't be the way back anymore if someone "outside" would just close the book. I was well aware of the risk, but I was coming inside the story anyway, but always with fear of no way back.