You beat me to making the thread, haha.
Sorry about that. I don't think I've ever had such a messy problem with a server before. Overnight a security patch was applied, and corrupted half of MySQL (our database). No data was lost, but nothing would load or work. After countless hours on the phone with the data center, and further hours personally working on it.... it's back.
And I managed to rebuild all the tables live, rather than restoring from backups, so nothing was lost.
Sorry again, hah. It's all good now.