How do I return to one page style rather than two page book style

without notice or warning my Libre Office documents are now in book form (two pages horizontally) rather than single page (vertical) format. I cannot find a way to alter or reverse this. It is very annoying and makes working difficult

Hello hydrant, on the status bar at the bottom of the window on the right side just before the Zoom slider, there are 3 very small icons that you can use to set the View Layout mode.

Click on the 1st of these icons to set the View Layout mode to Single Page