I tried to restart Opera and the computer...
Something must've got corrupted in your Opera settings or profile files that caused the browser to re-create them or the entire profile anew. Are your other bookmarks in place? History?
Try searching your system if the old profile or some files are still intact.
As long as the above is unlikely, there might be certain means to try - if there are some - finding some system copies, shadow copies. I don't know if there are ways to recover "unregistered" files - i.e. overwritten in the file system but not yet deleted physically (registry search for such clusters or something, then using some special applications, no idea).