Did you "reorganize" in Explorer/Finder?
Always reorganize from within LR. Otherwise, LR loses track of where to find your photos.
Thanks for your quick response. Yes, I reorganized in Finder, which I'll never do again. I read the link you gave me, but my images are not showing as "missing" in the library (there's no "!"). I can see all my images. After some reading last night, I also looked at the "Metadata -->Color Set" tab and it looks like they're all set to "default" and the colors are listed properly. Any thoughts?
If possible, I'd move everything back to where it was before. Move the files and load a backup of the catalog.
Then start over and move the files around from within LR.
If, during synchronizing, you did not select to remove missing photos from the library, then you should have the photos still in the library but with an '!' on each of the photos that has been moved and a '?' on every folder that has been removed. This leaves the option of moving everything back in place with finder(!) or update LR with the new location (right click ...).
If, during synchronizing, you selected to remove missing photos from the library and also selected to import new photos, then your edits and labels are gone for good.
THANK YOU SO MUCH!! I was able to restore all edits except for one day, which I hadn't backed up. I've learned a huge lesson and can't thank you enough for your help.