I've used Blender a bit, so I've been enjoying how usability has improved in v2.8, but I was in Animation view - timeline, dope sheet and view - and accidentally touched the keyboard - POW! The view changed to only the dope sheet. No menu items along the top, no '+' or little black rounded triangles in the corners to let me drag open new windows, nothing.
So I re-started, and got the menus back along the top; I can open the alternative views, but Animation is stuck on just Dope Sheet, nothing else. I have tried every keystroke/combination/mouse-clicks, but the only points on the screen where I get up&down arrow (indication I can click & drag) don't do anything. Just the Dope Sheet. How do I get more windows open?