Just a report and a solution on a nook glow light 3. I did some kind of gesture (I haven't re-defined them), and the screen turned upside-down. At some point I opened another book, and it turned that one upside-down too. Like it infected it
It didn't do it to all the books. When I re-opened those books, they remained upside-down, but not other books.
I fixed it by switching to landscape using the lower menu, which set it to normal landscape, then setting it to portrait. Fixed. I then did it to the other book also.