I got things back to normal by using the Window | Reset Window Layout menu option. I noticed that now the tabs for “Error List” “Output” “Pending Changes” etc were now at the bottom of their docked window rather than the top. I think I somehow or other must have created a second code window area and docked my error list window etc into that.
Incorrectly docked (tabs at the top):
Correctly docked (tabs at the bottom):
