Maybe you aren't 100 percent lucid ...anyways I know what you're talking about. In my first lucid I also felt these heavy feelings ...but not in my eyes ..mostly my body. It felt like I could end the dream at any moment by accident, and I was scared that it would happen. Well, the anxiety from these thoughts woke me up.

So next time just relax, try spinning around to improve your lucidity. Rubbing your hands works as well. Or in real life you could practice being more aware of things, when you see something pretty, like a flower for instance, take the time to really look at it ...touch it ..smell it. Appreciate your senses.

Hope this helps.