What is the cause of a headache during the practice of Shiva-yoga ?
It is due to tension. While worshipping Linga the whole body should be relaxed. If the body is tense, the mind also becomes tense. That tension falls upon the body. So, while looking at Linga, let your body be free, relax. Relax the whole body. Relax the mind also. If there are any bad ideas coming into the mind, you try to throw them. Relax the mind and relax the body. If there is no relaxation, there is tension. Headache is not a disease, it is due to tension, so relax your body, relax your mind.