wrong environment/view - all menus disappeared

Hi,

I suddenly landed in a total different view/mode where almost all of my menus are gone, I have no idea what it is. I’d just like to exit this mode and get back to the default view with all the menus. I also wasn’t able to fix it via saving the file and reopen it. I really hope someone can help.
This is what it looks like:


Press Shift+Space

Or try Ctrl-Arrow Up/Down.