Just checked the steering. After a night of sitting in my warm apartment, it's definitely looser, but it still feels kind of tight. There's no sound or grittiness, and no play, but it doesn't flop around like I'm used to on some of my other bikes. I think I'm going to take apart the headset and take a peek inside. Interesting points about the warm, humid indoor air infiltrating. Hadn't thought of that before, but I guess that's why there's such a thing as sealed bearings and headsets, right? Is there such a thing as sealed headsets? I'm so used to working on these older bikes that I don't really have a lot of knowledge about the newer stuff.
Thanks for the proffered suggestions. Hillrider, I'll make sure and check on this before doing anymore riding; thanks for the warning.