Shambhavi Mudra is an eye-crossing technique which is used as a hack to activate the parasympathetic nervous system—which is cognate with the medulla oblongata and the ajna chakra (or the so-called third eye). A sign that the mudra is being practiced properly is the result of having pressure build in the sinus cavities. To practice Shambhavi Mudra, gently look up and toward the forehead. GENTLY. However, there are similar benefits in the practice of simply keeping the eyes still during meditation—which technique can also be used as feedback for distracting thoughts so that they may be noticed more quickly (since distracting thoughts cause our eyes to “wander in the direction of the thoughts”). Focusing on the forehead too much may make the third eye pressure build to the point of a headache and it can be difficult to shut down. Perhaps one would be helped by eating or exercise to reduce that pressure. It is possible to build strength against the increased blood flow producing the head ache in the sinus cavities. The magnetic sensations resulting from Shambhavi Mudra are meant to draw and focus the mind in extremely powerful ways. Discovery of the third eye pressure is the discovery of the first of three knots which when unraveled result in the development of further spiritual faculties—the other major milestones in practice happens in the heart and the coccyx. I have read that there is deep archetypal significance in these unravelings. Anyone who has discovered this pressure through practice should be happy because Dhyana and the various Samadhis and bliss states are just around the corner. Watch out for very short and spontaneous breathless states with no thoughts in them. The breathless/mindless state is a door to Dhyana. And Dhyana is the door to Samadhi.