It was essential that he keep his eyes open. The enemy could try and breach the wall any second, a covert assault in the middle of the night would be tactically smart after all.
Every moment that passed, however, was like another bag of cement placed on his eyelids. No matter how many times he told himself he had to remain alert, no matter how many pinches he gave himself, it became harder and harder to stay awake.
Eventually, his eyes closed.
They opened shortly thereafter, to find no enemy.
Thus he felt no guilt every future time he slept…