It's happened to all of us: You zoom into a little space on your layout to check something, double-click in the drawing (either accidentally or on purpose), and end up in modelspace. If you're there on purpose, you can make your edits and be done, but if you've double-clicked by accident, you might not realize what's happened until you try to zoom out and realize you can't see your title block.
So, how to get back to paper space? You can't zoom out to see the viewport border, selecting the layout tab name won't do it, and you may or may not have paper and model toggles in your status bar (depending on version and status bar settings).
One way is to type PS (alias for PSPACE), but there's another nifty way too.
Instead of heading for the command line, go to the status bar and lock your viewport. Then you can zoom out, unlock the viewport, and reset the scale. (Locking the viewport again when you're done doesn't hurt, to prevent this sort of thing from happening again.)Just another proof that there's always more than one way to do anything in AutoCAD LT.