Lightroom :: Main Develop Module Controls Have Disappeared From Develop Window

The main develop module controls have disappeared from the develop window.  How do I recover them?  I'm working with Lightroom 5.3.  The missing controls are the sliders for exposure, contrast, clarity, etc.  I must have inadvertantly clicked something that made them disappear but nothing I've tried brings them back.  I've never had this experience in the years I've been using Lightroom (since version 1.1).