Sibi is a king in Hindu mythology. He became very famous as a protector of surrendered souls and a donor of charities.
Indra, the King of heaven once took the shape of a pigeon-hunter bird (eagle), and Agni, the fire-god, took the form of a pigeon. While being chased by the eagle, the pigeon took shelter on the lap of Maharaja Sibi, and the hunter eagle wanted the pigeon back from the King.
The King wanted to give it some other meat to eat and requested the bird not to kill the pigeon. The hunter bird refused to accept the Kings offer, but it was settled later that the eagle would accept flesh from the body of the King of the pigeons equivalent weight.
The King began to cut flesh from his body to weigh in the balance equivalent to the weight of the pigeon, but the mystic pigeon always remained heavier. The King then put himself on the balance to equate with the pigeon, and the demigods were pleased with him.
The King of heaven and the fire-god disclosed their identity, and the King was blessed by them.
The story has deep scientific and spiritual meaning behind it.
Explanation in Advaita Philosophy
To attain high level of spirituality, in an extreme parasympathetic state of mind, one needs to be disconnected with desires, expectations, ego and attachments to the worldly desires. The same is evident by Amarnath Ki Yatra where both Shiv and Parvati first leave Nandi (desires), then the moon (expectations), then Shesh nag (ego), Ganesha (relatives) and finally the five elements before they lose track of time (tandav nritya). These are the stages when one shifts from sympathetic to parasympathetic state of mind.
This is also true of the story of Dasura in Yoga Vasishtha, where sage Dasura to get detached with his father’s death first offers his organs in the fire one by one and later sits on the tendril under the Kadamba tree and performs Gomedha, Aswamedha and Naramedha before getting enlightenment.
Cutting your organs denotes detachment with the organs one by one and then by yourself in an extreme parasympathetic yogic state of mind.
Sitting on the tendril means that you are in a state when you have forgotten about your body and merged with the sukshma sharira.
Gomedha, Ashvamedha and Naramedha mean totally getting control of your chitta, sense and the body.