Theory: Svarbhanu’s True Motive
Perhaps Svarbhanu, the Raksasa Asura who attempted (and succeeded) at partaking of the amrita, the nectar of immortality, didn’t actually want immortality, but rather undefeatable power and prowess, as found in the Kundalini energy which Rāhu represents. Rather than through the immortalizing effects of the nectar, it was actually through his beheading itself in he actually achieved his true desire: power which not even Sūrya and Candra could best, the ability to shadow the luminaries (which Svarbhanu achieved by their own actions). In a way, Rāhu’s very existence is purely a result of their oppression of the Asuras. Karma, baby. I call that a self-fulfilling prophecy.