Laughter yoga (Hasyayoga) is a modern exercise involving prolonged voluntary laughter. This type of yoga is based on the belief that voluntary laughter provides similar physiological and psychological benefits as spontaneous laughter. It is usually done in groups, with eye contact and much playfulness between participants. Intentional laughter often turns into real and contagious laughter.
Laughter Yoga was popularized by family physician Madan Kataria who modernized and simplified the work of earlier laughter pioneers,  who taught very similar concepts starting in the 1960s. Madan Kataria wrote about his experience in his 2002 book Laugh For No Reason.
The yoga is performed without any humorous reason to laugh, with one practitioner observing that "The mind does not know that we’re faking it."
Laughter yoga sessions may start with gentle warm-up techniques which include stretching, chanting, clapping, eye contact and body movement, to help break down inhibitions and encourage a sense of playfulness. Breathing exercises are used to prepare the lungs for laughter, followed by a series of ‘laughter exercises’ that combine the method of acting and visualization techniques with playfulness. Laughter exercises are interspersed with breathing exercises. Twenty minutes of laughter is sufficient to develop fully physiological benefits.
A 2019 review and meta-analysis in the field of laughter-inducing therapies suggests that they are more effective than humorous laughter can improve depression. However, overall study quality was low. 
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