People can I please advise you to make sure you are first very well established in the first 2 levels of Yoga before you embark on any Pranayama (breath-control). First be steeped in Yama(abstinences - alcohol, drugs, sex, meat, etc) and Niyama(observances - love, kindness, non-harm, patience, etc) before moving on to asans(postures) and especially pranayama. Every swami will tell you that if you are not living a committed Spiritual life in every respect, then practicing the 4th level of Yoga - breathing exercises, especially the advanced ones, can potentially be harmful. You should really only practice techniques like this within the framework of a spiritual society and Guru-disciple relationship. Breathing techniques force prana up the subtle spine, thus awakening higher and higher chakra's. This process should occur naturally and gradually as part of a disciplined spiritual life - it should not be forced.