Conquering death through Yamas and Niyamas
Indian Mythology has a lot of 'Sukshmams' which means subtleties in the plots. For example the density and interconnection in the plots in Mahabharatha, the longest and one of the greatest epics in the world is far more that that in any mystery or detective novel.
We saw one symbolism of Pashasana in the presentation titled "Mythology and symbolism behind Asanas-1" (video audio recording at 27:10).
One practical benefit of doing Pashasana is that by learning to relax in a deep twist like Pashasana and breathing normally, one is able to handle difficult situations like physical pain, being in a MRI machine etc. with a lot more ease than without this training. The symbolism is that when Yama, the lord of death (and also the lord of fairness and Dharma) casts his celestial Lasso called the Pasha to retreive the atma, one is able to let go if the body with a lot more ease.
Yet another symbolism of this pose is found in the Yama Gita. Most people are familiar with the quintessential gem of the Mahabharatha, namely, the Bhagavad Gita. There, however, are several other Gitas. The Ashtavakra Gita, a dialog between Sage Ashtavakra and king Janaka is one. The Yama Gita, a dialog between Yama and his assistant is another. It comes in the Vishnu Purana. When Maitreya asks his teacher, Sage Parashara, if a human can conquer death in a lifetime, Parashara tells him that the same question was asked of yore by one of the Pandava brothers, Nakula, to Bheeshma. The story goes as follows. Once Yama saw one of his assistants cast the pasha on an ardent devotee of Vishnu. He stops the assistant from completing the act and whispers in his ear the Yama Gita. Yama tells the assistant that while it is acceptable to judge people by their karma and retreive their atma, at the time of death, using the Pasha, it is not acceptable to cast the Pasha on a Vaishnava. When the assistant asks him who a Vasihnava is Yama explains to him that it is a person who follows various precepts and observances that today we have come to know as the Yamas and Niyamas of Maharishi Patanjali. Such a person gets a special passage to Vaikunta or Liberation .