"It is a way to do movement," she said. "If you're stressed out, you're not taking care of yourself. You can't get fit until you get balanced."

Humor can boost the immune system and lower blood pressure, according to the Centers for Disease Control, and laughing for 10 to 15 minutes a day can burn 10 to 40 calories.

Gregory Chertok, sport psychology counselor and fitness trainer at the Physical Medicine and Rehabilitation Center in Englewood, New Jersey, said there is a staggering amount of documented findings on the importance of mood to behavior.

"It (laughing) is not like doing a cardio workout or a plank (exercise)," said Chertok, who encourages his athlete clients to notice their moods. "It's less of a physical, more of a social, benefit. Engaging with people is an enjoyable thing."

Chertok noted that writer and researcher Norman Cousins, whose book "Anatomy of an Illness" influenced Kataria, famously referred to laughter as "internal jogging."

He said the Self-Determination Theory, a psychological theory of motivation, says that anyone seeking a healthy lifestyle must feel three things: autonomy, competence, and relatedness.

"A person who is not physically able to do more strenuous yoga may feel more competent and related in a setting like this (laughter yoga)," he said.

Of course, as Pandora discovered to her dismay, even openness has consequences.

"You cannot open up your box of emotions separately," Gendry explained. "Laughter and tears go side by side. The more you laugh, the more you cry. You can't avoid that."

(Editing by Patricia Reaney and Leslie Gevirtz)