Sayana refers to the reclining posture of the Lord. Sri Anantha Padmanabha had given darshan to many rishis like Divakara Muni and Bilvamangalam Swami in the forest, once known as Ananthan Kaadu. The story goes like this:
Divakara Muni was a pious sadhu of the Tulu community. Once when he was doing puja, a little boy entered his room and started playing with him. The sage was so attracted by the boy that he wanted to keep him. The boy agreed on the condition that he should not be scolded under any circumstances. The boy used to play with puja items and indulge in mischief. One day he playfully put the Saligrama in his mouth. This angered the sage and he chided the boy. In no time the boy disappeared saying ``if you want to see me again, come to Ananthan Kaadu. Divakara Muni realised that it was Lord Krishna who had come to him in the guise of the boy. The sage went in search of Him. He found the boy, but he disappeared into a huge Iluppa tree. The tree fell down in the form of Lord Vishnu in Ananthasayanam posture.
According to legend, this colossal divine form was several miles long stretching from Thiruvallam to Thiruppapur. This same form was taken to the present temple and was being worshipped till the time of Marthanda Varma. During his reign, the king renovated the sanctum and reinstalled a new image, made out 1,200 Saligramas with a special mixture. A poor Ezhava couple had darshan of the Lord as a small child, who had gruel from their hands. Justifying this legend, even today, the rice Neivedyam is offered to the Lord in a coconut shell, made of gold.