He taught young volunteers, mostly secondary school students, the techniques of Laughter Yoga. The volunteers would then go on to teach the elderly at nursing homes and public recreational areas over a two-year period.

"Hong Kong to me is a very stressed society and pressures are always very high socially, politically and financially," Kataria says. "I think Hongkongers need Laughter Yoga very badly… We have all been taking life too seriously and time has come to take laughter seriously."

Originally a medical doctor based in Mumbai and a writer for a health magazine, Kataria first had the idea of forming a laughter club in 1995 when he was writing about laughter being the best medicine.

"Many researches have been done on the benefits of laughter but nobody laughs in Mumbai," the 59-year-old recalls. "So I thought, why not start a laughter club?"

He started the club by sharing jokes with a couple of friends and after 10 days, the group quickly expanded to 55 people. Yet Kataria was running out of good jokes to keep everyone laughing.

"I then found studies showing that your body cannot differentiate between real and fake laughter, so you still get the same benefits if you're pretending to laugh," he explains.

"Based on this idea, I came up with the concept of Laughter Yoga, where we laugh for no reason."

As a regular yogi, Kataria combined laughing and breathing exercises together, which helps bring more oxygen to one's body and brain and exhale stale air out of the lungs.

Held in public parks and free for anyone to join, Laughter Yoga spread very quickly. Inspired by this success, Kataria stopped his medical practice in 2001 and started travelling around the world to teach the technique.

Although Laughter Yoga is not difficult and can be practised by anyone, we need to learn how to do it properly to get the most benefits, Kataria says.

All laughter clubs are social clubs and do not charge any fees; Kataria earns his money only through teacher training.

"I travel the globe to train other people as leaders and to make people aware of the benefits of laughter. My students then go on to train others. I have the best job in the world - I laugh and get paid [for it]," he says, laughing.

"I never thought it would become such a big movement. I think anything good for society spreads by itself. Since I'm not putting my business behind it but just giving it away for free, it's easy for everyone to practise."

As it is difficult to make people laugh without a reason, a typical laughter yoga session starts with some warm-up exercises such as clapping, deep breathing and yoga stretches. Then, the fun starts: participants role play and laugh together.

"When you laugh as a group, it quickly turns into genuine laughter," Kataria explains.

The most significant difference between laughter yoga and its traditional form, according to Kataria, is the level of seriousness.

"Yoga is serious and people don't laugh much; laughter yoga, on the other hand, is not serious at all and it's a lot of fun."

Poon Tat-cheung, 68, and his wife Chau Si-wang, 73, could not agree more. Three years ago, the retired couple heard about laughter yoga from a friend and since then have been attending weekly laughter clubs in Yuen Long Park and Kowloon Park on Saturday mornings.

"I find myself healthier and more cheerful," says Poon. "The teachers in the sessions learned from Dr Kataria and are certified. The lessons have a lot of freedom; you can add anything, as long as you keep on laughing."

"In the past, I was very shy and dared not speak to people," says Chau. "Now, I'm more open and cheerful, I smile and say hello even to people I meet for the first time."

Don't worry that your laughter is fake or forced, it still has solid benefits.

• Practising in a group makes fake laughter become natural laughter very quickly.
• Benefits will only come when you sustain your laugh for 10 to 15 minutes. Natural laughter only lasts a few seconds, which is not sufficient.
• A group of 10 to 15 people is a good size but the more the merrier; when a group is large, laughter becomes easier.
• After you learn the techniques you can do it by yourself at home - sit down in one corner and go "hahahaha". Like riding a bike, it's a technique you can learn and never forget.

• It changes your mood by releasing endorphins - the feel-good hormones - from your brain cells. When your mood is good, you do everything well.
• Scientific studies show it reduces all kinds of stress levels and also strengthens the immune system.
• It is very energising because it's an aerobic exercise - your brain gets more oxygen and your efficiency increases.
• It's a great connector. Everyone wants to be with happy people, so if you practise Laughter Yoga you get into the habit of laughing more and you get more friends.
• Regular practice gives you a positive mentality and you learn to laugh even when you face difficulties and challenges in life.