I haven't done anything to it in the last three days! There's no reason for that! So I panicked, and LaCie's support site wasn't helpful and said I should buy some crazy disk utility.
But then i remembered that OS X has it's own disk utility thing, so I just ran that, and it fixed it right away, after about 20 seconds of me staring at it, wringing my hands.
*faints* 159 GB of crap, people, is what was at stake here. Some googling informed me that mp3s with illegal characters are probably the culprits. So anyway, i'll just be burning shit over here.
Speaking of techie woes, is anybody else having the problem where Firefox won't let you click in text boxes until you click to another program and back again? it's totally irritating.