Why do i look sad, while doing things consciously?

I have started doing things consciously, i don't want to laugh anymore, i just want to maintain that inner peace felt in doing things meditatively. But people have started asking that "i am looking sad". Should i smile or should i go with the flow, i want to follow Lord Buddha. One more thing i want to know the Essence of Lord Buddha with in few lines, i theoretically know only about focusing on breathing and vipassana meditation(which i am going to attend soon)