Always be happy
Simcha
Rebbe Nachman taught that being joyful at all times is a great mitzvah, and that one must use every strength to push away sadness and depression. Many illnesses, he said, stem from a lack of joy, and joy has the power to heal. When happiness does not come naturally, a person can even act happy – sometimes with a bit of silliness – until true joy follows.
Source: Likutei Moharan II:24