He found them
Were very heavy.
They did not know
What to say to him.”
καὶ πάλιν ἐλθὼν εὗρεν αὐτοὺς καθεύδοντας, ἦσαν γὰρ αὐτῶν οἱ ὀφθαλμοὶ καταβαρυνόμενοι, καὶ οὐκ ᾔδεισαν τί ἀποκριθῶσιν αὐτῷ.
This is almost word for word in Matthew, chapter 26:43, but there is an addition about the apostles being embarrassed and not able to say anything here. In Luke, chapter 22, and John, chapter 22, there is nothing more about these 2nd and 3rd visits of Jesus. Mark recounted that Jesus again came (καὶ πάλιν ἐλθὼν) and this time he again found his 3 disciples sleeping (εὗρεν αὐτοὺς καθεύδοντας), because their eyes were heavy or overburdened (ἦσαν γὰρ αὐτῶν οἱ ὀφθαλμοὶ καταβαρυνόμενοι). This was the 2nd time that he found his 3 trusted apostles sleeping. There were no excuses, except that they were tired. They did not know what to answer to Jesus (καὶ οὐκ ᾔδεισαν τί ἀποκριθῶσιν αὐτῷ). They had failed to stay awake and be vigilant, pure and simple.