why your eyes/head feels weird when you wear glasses without needing them or with the wrong prescription
The lens in your eye is supposed to be shaped like a cool spherical ball. Some people have very slightly oval shaped lenses, so the glasses are made to distort the image in the correct way. So if you have a skinny and tall lens in your eye, the glasses try to distort it in a fat and wide way, and vice versa. But if you have a different shape than the glasses are meant for, it’s not gonna work.
Glasses don’t just correct for vision problems, they also distort what you see. As you move your head around, this distortion means the way the image looks is different depending on the prescription (or presence/absence). If you wear glasses and get a different prescription, this is noticable at first, but the brain is really good at “correcting” for it, so you stop noticing it after a while.
You’re feeling the muscles that control your eyes struggling to adjust them, to bring the image into focus, which isn’t working.