After all, he said to himself, it's probably only insomnia. Many must have it.

excerpt from an awesome analysis of Hemingway's "A Clean Well-Lighted Place" :

Another tool used by Hemingway in this story is the image of Nothing. Nothing is what the old man wants to escape. The older waiter, who sometimes acts as the voice of the old man's soul, describes his adversary:

"It was all nothing, and a man was nothing, too...Some lived in it and never felt it but he knew it was nada y pues nada y pues nada. Our nada who art in nada nada be thy name thy kingdom nada they will be nada in nada as it is in nada. Give us this nada our daily nada and nada us our nada as we nada our nadas and nada us not into nada but deliver us from nada; pues nada. Hail nothing full of nothing, nothing is with thee..."

The Nothing is a relentless monotony, unbroken by joy or sorrow. It is unending emptiness without comfort or companionship of man or God. It is the senselessness of each heart-beat that is just like the last and refuses to give in to death. The old man's loneliness is empty. His days of retirement without useful work or purpose are empty. The emptiness of a life without progress of meaning is Nothing, and this Nothing afflicts the old man with a powerful grip. The only escape from this Nothing is blissful unconsciousness, permanent only in death.