Moving the lights/plugs seems to have done the trick. The past two nights have been pretty good, though incidentally, now I have a cold.
I think I'll hold off on the vitamin D for 3-4 more weeks, just so I don't fall prey to trying too many new things at once. It makes it too difficult to associate effects to their causes. I will give it a shot, however, and use it at least until Spring is in full bloom.
And yes, I'm actually holding that handstand. Get on my level.