योगश्चित्तवृत्तिनिरोधः means - a process of blocking the patterns of awareness, here I must be clear that - it means not the blocking of awareness but blocking of ways of it. 

• As in meditation - awareness is present, but patterns are blocked/absent.
• When the flow or patterns of consciousness is blocked, we can achieve a different and fundamental state of consciousness.
• Chitta means individual consciousness. It includes- consciousness state of mind + subconscious state of mind + unconscious state of mind.
• Chitta = pure consciousness or = individual consciousness. It includes three types of consciousness and three states of consciousness.
• Then one more question arises- what is mind? The mind is just an instrument of knowledge, which sees the Chitta and perceives it according to choices/ stored sanskara.
• Another question: What is consciousness? Consciousness is unimaginable, beyond the body, within this body, sometimes outside this body. It is infinite, eternal or can say - Ananta. It is like a thread connecting many lives and incarnations.
• For clearly understanding, we must know about -- what is Vritti? As we know, Vritta means circle. Hence Vritti means circular, as waves instil / pond water. 
• Chitta Vritti = attitude of Chitta or we can say modes of mind.
• Blocking of the patterns arising in all the dimensions of consciousness and due to this blocking expression of individual awareness (arising in different places) transcended. I think it is the right meaning of योगश्चित्तवृत्तिनिरोधः
• Because there are five stages of mind (according to Phys) and five types of Vritti, once they block one by one, we can reach step by step at the stage of samadhi or merge with super consciousness - the final aim of yoga.

read less

Jai Gurudev Hi Kamal, As you might be aware that Yoga Asanas deliver better results when you practice it correctly otherwise it can harm you more than you expect. Recent studies have indicated that around 10% of new yoga practitioners are getting hurt due to wrong way of doing Yoga Asanas and other wings of Yoga like pranayama, diet practices and meditation etc. Apart from the way you practice yoga, there could be other reasons likes your physical fitness, your condition just before you start yoga practice (like low glucose level), hydration levels during and after Yoga practice, severity of Yoga practice etc can also cause you headache. Studying carefully how you are doing yoga asanas and stress on your nerves, and other factors I mentioned above guiding on those lines might help you to get rid of it. However it has to be dealt case to case basis when supervised personally. Try to bring the changes suggested above and let me know if you can see improvement. Wish you happy recovery and happy Yoga practicing!!! Jai Gurudev!!! read less