Test post.
Then that post and the subsequent one (by someone else) appear in the thread but aren't listed when I go to my 'Subscribed Threads', or to the list of my recent posts that appears from clicking my username. I thought this might resolve overnight, but no.
That post has a photo so the post is listed in my list of recent attachments, but the post is not listed in my subscribed threads or personal posting history.
Okay, this may have worked. Basically, the database has a bunch of tables, and one of them (an important one, obviously) got corrupted. It was able to fake it for a while, but then it decided it had enough and gave up. The table that was corrupted was nearly 3.5 gigs in size, so it took an entire hour to check and repair, which we've now done. Going to keep an eye on things for a while more, but we should be back to operating as normal.