One of the most publicized photos of shows a British trench during a lull. Note those "resting", two of them on the floor of the trench. One rifleman remains on guard in case the enemy decides on a sudden attack.
Guerra e Luoghi British soldiers resting in sleeping shelters in a trench. Battle of the Somme,September type of "accommodation" left a lot to be desired, Sleep deprivation was one of the most serious side effects of trench warfare.