Matthew 26:43

And he came again and found them sleeping, for their eyes were heavy.

Note again the time-lapse between the second and third utterances of the prayer. Although he used the same words, Christ did not pray rote prayers. That the disciples actually tried to stay awake may be assumed, since they had so boldly proclaimed their loyalty only a little earlier. As extenuation, the hour was long past midnight. Very strong emotions had attended the Last Supper, the identification of the traitor, and the contemplation of Christ's death. Also, the crowded events of that entire week had left them physically and emotionally exhausted. "For their eyes were heavy" shows the strain under which they had arrived at that dark hour.