Awareness in Salamba Shirshasana

This pose is very difficult to accomplish. While practicing this pose, I definitely feel an uncomfortable pressure on my head and shoulder blades, and slightly dizzy/light-headed from being upside-down. However, after a fixed period of time, it calmed my state of mind, and I felt more awake when exiting this pose. I tend to lose my balance if I try to go to full posture, and have a lot of difficulty with keeping both legs together if trying to lift up.