I took it to the Apple Store, where at first the woman I talked to thought the same thing I did--that the connecting cable for the display was probably loose or something. But she took it in the back, and then told me it was water damaged and they'd have to charge Apple's $750 flat-rate water damage repair fee, and send my laptop out to get checked over, and replace the logic board and.........
So lol no I don't have $750 and I can't be without my laptop because my entire job and like 70% of the rest of my life is on the damn thing. And while she showed me a picture with "water damage" it seemed to me like it was just the "water has existed near this computer" sensor or something. So I ordered the special screwdrivers from Amazon and on Monday I opened up the back, unplugged the connector to the display, plugged it back in, restarted the computer and........it seems to be working fine?
I'm still a little wary and I'm keeping my fingers crossed, but I seem to have dodged a bullet.
(also, wtf Apple, seriously?)