However, once I raised his head's smoothness, I noticed that I didn't really change the face I wanted, so I went back and did the same thing with his smooth face (which literally took hours and hours to do).
Once I finished my ridiculously tedious task, I returned to his expression controller and went to put his face back on low-poly, but nothing happened. None of the controls worked anymore. I tried moving his controllers (joints? not sure what they are called), but those, too, weren't connected. I have no clue what changed, since all I did was apply a different texture to his face.
Anyway, here's a picture of what I mean, since I'm not sure if you guys would understand me.
This is him with his controllers in the place they should be, yet aren't connected.
This is me moving the connectors to where they should be.
Thanks for any help you guys could have! My animation was going amazingly until this, and now it doesn't at all.