Photos have gone missing from main library

Hello everyone,

I have been using Lightroom CC for a while now and had accumulated 20K+ of photos.  When I opened the program yesterday, it looked totally different and there were a total of 393 photos.  Some of the photos I hadn't seen in a while, some were much newer - taken this past weekend.  To my knowledge, I did not do anything differently opening the software than my normal procedure.  I believed that all my photos were backed up in the Cloud, but whether I select "Cloud" or "Local", the same 393 photos appear, not the 20K+.  I'm desperate to recover the photos - any suggestions would be helpful.

Also, some of the posts that I have read talk about backing up a copy of the Lightroom library from time to time.  I assumed that the "Cloud" was my backup.  How do I back up a Lr library in Lr CC?

Thank-you in advance.