Workspace issue

I have been using Sigil for about a week and from the beginning the Preview window was fixed on the right side of the screen.

When I was going to make several changes to the book's html file, I'd click on F10 for disabling the preview mode so that it wouldn't keep updating (and freezing for a couple seconds) all the time. Then when I clicked on F10 the Table of Contents window took the place of the Preview window, and the window with the HTML code remained fixed in its dimensions.

However, now when I click on F10 the Preview window simply disappears the window with the HTML code readjusts itself to the PC screen. And that is driving me crazy. :knife:

I must have clicked on something to cause this problem, but I have no idea what happened. :smack:

I have been searching this forum and could not find a solution.

If anyone has a tip on how to configure the workspace to get it back to the old way, I would greatly appreciate it.

:help:

I am on Windows 10.