Ah Ha! Now I get it.

When reading the Epic of Gilgamesh, where he was trying to find the secret to eternal life from Utnapishtim I didn't understand why Utnapishtim would set forth the challenge for Gilgamesh to stay awake. Sometimes I guess I just need to have things spelled out for me. Here, in what is a children's version of the story I got it. Sleep was considered a "little death".

The Sumerians were not alone in their opinion of sleep.  According toG. de Purucker, "Sleep and death are brothers, according to the old Greek proverb." He claims that sleep and death are virtually identical, death being the "perfect sleep." Framed with this belief I can see how staying awake would be a fitting test, though not very easy, or reasonable considering Gilgamesh's worn out state.

Greek Gods of Death and Sleep, Hynos and Thanatos

Here, Hypnos and Thanatos are describes as twins even. These beliefs have even made their way into Christianity in very interesting ways. " the Angel of Death Thanatos inherited from Zeus his role as a judge of who shall live and who shall die, and he did this by weighing the living on a balance scale. Centuries later Christians would depict St. Michael the Archangel at the Last Judgement wielding a sword in one hand and with the other weighing the souls of the dead in a similar balance scale."