I was working on a file when I suddenly hit something that closed the file.
When I reopened, there were two versions of the same data -- One with the
file name plus the extension :1 and the other :2. If I close one, the other
closes. If I try to save one file to another file name, I still get two
versions with :1 and :2 in the new file name when I open that file. Only one
file name (without the :1 or :2 extension) shows up on my directory. What
have I done? How can I go back to having only one version of the file?

(I've been using Excel for years and never had this problem. I could find
nothing about it in the Help menu. Any guidance will be appreciated!)