Working in model space and while clicking the mouse I accidentally hit a couple of unknown keys and everything disappeared.  I tied an undo and another and another, but cannot get anything in model space to reappear.

Items in paper space are visible.

All layers are on and thawed.  What could have possibly happened?  No new lines or text will appear either.  Although when I press 'command +a' the new lines I drew appear as dotted lines and the properties box indicates  a 1084 items are selected, but only the new 3 or 4 lines become visible.  

Please somebody know what to do.  A whole day of drafting is about to be lost!

Thanks,

John