Left Click on the almost invisible icon just to the left of the Editor title (top left of frame). You can then drag the Editor panel back to the top left next to Mixer where it normally sits. The place where it is going dock itself turns dark blue. Let go the mouse button and it should dock where you put it but full size again.
Alternatively if you go to the Workspace drop down menu (top right) and select 'Default' you should go back to the default workspace but, of course, without any of your customisations.