Which snake does Lord Vishnu sleep on?

You may have seen the beautiful images, deities, and paintings of Lord Vishnu portrayed as reclined on a coil of the body of a big snake in the middle of the ocean of milk (Ksheer Sagar). It has multiple hoods spread across the entire body of the Lord, giving Him all protection. This snake is not an ordinary one but is the eternal servitor of the Lord and is called Sheshanag or Anantashesha. Whenever and wherever there is a decline in religious activities and a predominant increase in irreligiosity, the Lord appears to re-establish the principles of Dharma. But He does not come alone. He comes with His eternal associates that serve Him in different forms of loving exchanges in Vaikuntha. For example, when Lord Krishna, the Supreme Personality of Godhead, appeared on the earth in Dwapar Yuga, Sheshanag came in the form of Lord Balaram with him.

What is the power of Sheshnag?

The Vedic scriptures mention that Sheshnag is the immediate expansion of Lord Vishnu who serves Him with pure devotion. The Acharyas in the path of Bhakti also explain that Sheshnag represents the Guru Tattva. Without the mercy of Guru, the living entity cannot attain the lotus feet of the Supreme Lord. Sheshnag comes in the form of Balaram or Lakshman in the pastimes of Lord Krishna and Lord Ram respectively. Without pleasing Balaram, one cannot understand the nature of Lord Krishna, or without pleasing Lakshman, one cannot know Lord Ram. Similarly, if one wants to serve Lord Vishnu, the mercy of Sheshnag is needed. When it is achieved, Lord Vishnu, without any delay, accepts even a fallen soul and gives Him liberation from all kinds of suffering. Such is the power of Sheshnag.