That varies wildly by the design of the glasses. I tried rock climbing once with my glasses instead of contacts and it was intolerable. It wasn't immediately obvious how often I relied on a quick flick of the eyes to the outer edges until I tried it.

As to the original point, people adjust their head position all the time without even thinking about it. It's an unnatural and conditioned response to hear a noise on your right rear and move a joystick or mouse to look for the source of the noise.