Doh!!
Yes, I looked at that before, but glossed over it since I had NOT made any changes there previously, or ever.
I played w/ it last night, and changing to "Preview on he Right" did NOTHING, but thankfully selecting "NONE" got me what I wanted.
I guess somehow the setting changed...
I liked the way it was before it suddenly changed without my intended input (email list on left, with selected viewed content on the right side), but I don't see a way to switch the presentation.
Now, only a few emails are listed on the top, and a portion of the selected email is shown below...