Five days a week, at councils on aging around the North Shore, Dot McKeen teaches people how to laugh. And to stretch. And to breathe. Her expertise is laughter yoga, also called Hasya yoga, which has grown worldwide since it was founded in 1985. According to Laughter Yoga International, there are more than 6,000 laughter yoga clubs in 60 countries. Health benefits include stress reduction, strengthening immune systems, increased lung capacity, and aerobic exercise, which stimulates the heart and increases blood circulation. Also, the instructor added, it improves sleep patterns and provides relief from depression and anxiety.