It's so difficult for me to be in Yoga Nidra

While doing Yog Nidra, the more I try to detach from the body and stay calm, the more body conscious I become. I feel itchy, thirsty. Half way through Yog Nidra, it feels as if my arms have become very heavy and it starts hurting. In panic I move them. How to come out of this? Do we have to complete Yog Nidra even if we move in between or we should start afresh from the beginning? Visit http://www.gurumaa.com for more videos