Maybe like me you were straining yourself too hard in some way, like maybe breathing too hard. Try toning it down a little, relax to the point where you're no longer getting this pain.

With ANY form of meditation, the most important thing is not to worry about whether you're doing it right, not to judge yourself if you're getting off track or if you think "nothing's happening," etc. This seems to be the sort of technique that calms your body down first, enabling you gradually and automatically to stop "thinking about stuff." But thinking a lot is a common problem for anyone not used to letting go of thoughts. Every time a thought arises, just notice it, and nonjudgementally bring yourself back to the "task" at hand (paying attention to your vision, to your breath, whatever it may be).

Thinking about whether you're doing it right can become just another THOUGHT (obviously) and just another distraction. Don't let it affect you too much because any technique, if you are focusing on one aspect of your experience, can have beneficial effects, whether you are doing it the same as other people or not. And remember that EVERY thought must be forgotten, and let go of, eventually... so why not right now?