I don't know what happened, but I was trying out a piece of AJAX software called Relay and I installed it in my web app under the directory /relay. I created a database for it, but decided that it really wouldn't work in my situation so I deleted the directory /relay and deleted the mysql database for it.
Now all my post pages in WP are missing! They show up in the sidebar (they're all still in the database) but I can't pull any of them up individually or in the admin console (it just shows "No posts" when I try to edit them.
My website is down now because something got hosed in this, but I cannot, for the life of me, imagine what got messed up so much that the posts are all still happily in the database, but completely unaccessible to WP. Everything else is fine. Categories, links, Pages, etc... It's just the posts!