The Yoga of the Supreme Person 16. The Divine And Demoniac Natures 17. The Divisions of Faith 18. In this verse Arjuna is referred to as Gudakesa. Gudaka means sleep, and one who conquers sleep is called gudakesa.
Sleep also means ignorance.
So Arjuna conquered both sleep and ignorance because of his friendship with Krsna. As a great devotee of Krsna, he could not forget Krsna even for a moment, because that is the nature of a devotee. Either in waking or in sleep, a devotee of the Lord can never be free from thinking of Krsna's name, form, quality and pastimes. Thus a devotee of Krsna can conquer both sleep and ignorance simply by thinking of Krsna constantly. This is called Krsna consciousness, or samadhi.