Story:

Apasmara repented to the Hindu Gods, and he gave gifts, to impress them. In return, he was granted the gift of giving seizures and epilepsy. He misused these gifts, and inflicted the Goddess Parvathi, the wife of Lord Shiva. As punishment, Lord Shiva, who transformed into Nataraja (the Lord of Dance), eternally stands on top of Apasmara. Crushing the demon, below his foot. The meaning is supposed to show that ignorance, epilepsy, laziness, and all neurological disorders, are not things that the world can ever be rid of. This is because if Apasmara is killed, then there will be an unbalance between knowledge and ignorance. Knowledge cannot be gained without effort or struggle. Lord Shiva (Nataraja) therefore suppresses the amount of such negative things, by standing on Apasmara eternally.