When reading on my iPad/iBook - often the pages will revert and flip back 100 or so pages.

When reading on my iPad/iBooks, the pages often revert back 100 pages - at no particular spot, and not aware I did anything to have caused this.

Extremely frustrating, as I have to flip pages forward to get to what I was reading. WHAT AM I DOING WRONG - WHAT IS GOING ON????