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, qualities 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.

From Srila Prabhupada’s purport to Bg 1.24