Of course, a little fun and laughter is good, occasionally. But don't let light mindedness possess you. I, too, like to laugh sometimes, as you know. But when I choose to be serious, nothing and no one can draw me out of my inner Self.
Be deep in everything you do. Even when laughing, don't lose your inner calmness. Be joyful inside, but always inwardly a little withdrawn. Be centered in the joy within.
Dwell always in the Self. Come down a little bit when you have to, to eat, or talk, or to do your work; then withdraw into the Self again.
Be calmly active, and actively calm. That is the way of the yogi."
~ Paramhansa Yogananda