I am happy and calm now. What can I do to maintain this state throughout life?
Share it with more and more people. Joy or wisdom if not shared with others starts dwindling. Now this does not mean you go to others and start teaching them Bhastrika Pranayama, or the Sudarshan Kriya. Unless you get properly trained, you should not go about teaching meditation and these practices to others. This is why we had to put a quality control for Yoga in the country today. There is a QCI (Quality Control for India) body and the government has asked it to do something for Yoga also. It is because it is observed that people learn something from somewhere and then go around teaching it to others without proper training. Then when some unwanted or unexpected things happen it becomes a problem. There is a proverb in Sanskrit – “Yasya kasya tarur-mulam yena kenapi churnitam; yasmai kasmai pradaatavyam yatvaa-tatvaa bhavishyati” (From the Subhashita). It means that someone may bring the root of any tree, grind it into a fine powder and give it off as medicine to others. And something or the other may happen to the other person by taking that (untested) medicine. The same is what is happening with Yoga also these days. People practice Yoga for just a week and proclaim themselves to be Yoga instructors and teachers. There needs to be a proper quality system in place for Yoga also, and there should be levels or stages of training and certification. Until then, do not just go and train others. But you should always talk to other people about Yoga and bring more awareness about it. You should definitely inspire and encourage others for this.