Wow! All my categories have vanished. I can't see any in the Categories | "All Categories" tab in the Edit Post screen; I can see 10 in the "Most Used" tab.
All the Tags have disappeared, also. I can still see them in the Tag Cloud in the sidebar and select them in the Edit Post screen but none appear in the published post.
All published posts now lack both Categories and Tags, though all had them assigned until about yesterday. I think it happened today.
I've tried applying categories and tags to a recent post but they don't stick.
Can anybody tell me how to restore them, please?