If those still living neglected their dead, and did not leave them funerary offerings/kipsu, the spirit of the departed might wander about, come above, and haunt the upper world. Kipsu consisted mostly of food, drink and oil. If one did not have any descendants to leave offerings, one was sustained in the Underworld with dust and scraps.

Stillborn children and those who “died before their time” were the only ones to escape such a fate. They played at a “gold and silver table” and feasted on good food. These are the only exceptions that Mesopotamians had, no doubt to offer some solace to grieving parents.

The Sumerians had different names for this other world. They were: arali, irkalla, kukku, ekur, kigal, ganzir. All of these names were later borrowed by the Akkadians. Simply, it was also known as “earth”, “ground”, “the land of no return”, “lower world” or occasionally, “desert”.

We learn about the taboos the living who enter the underworld must adhere to in the myth “Gilgamesh, Enkidu and the Nether World”. In it, Kramer states, “There were certain taboos, however, which, according to the author of the poem, anyone wishing to descend to the nether world must beware of violating: he must not wear clean clothes, anoint himself with “good” oil, carry a weapon or staff, wear sandals, make a noise, or behave normally toward the members of his family. If he broke any of those taboos, he would be surrounded by the ‘stewards’ and by the shades inhabiting the lower regions and would be held fast by ‘the outcry of the nether world’.” (Samuel Noah Kramer, “The Sumerians” © 1963 by the University of Chicago, pg 133.)

Sources:
Samuel Noah Kramer, “The Sumerians” © 1963 by the University of Chicago, pg 133
Jeremy Black and Anthony Green “Gods, Demons and Symbols of Ancient Mesopotamia”, ©1992 by the Trustees of the British Museum pgs 27, 28,180, 181