The Na'vi prefer to sleep in large groups for physical closeness and comfort. This arrangement also acts as an effective early warning system in the event of danger. Families sleep together on larger hammocks, which are decorated and meticulously constructed for flexibility and strength. The Na'vi call the large family hammock eywa k'sey nivi'bri'sta, which translates roughly into “safe in the arms of Eywa,” or more literally as “Eywa cradles everyone.” For everyday use, the family hammock is known simply as nivi, or “us.”
Clan members will occasionally sleep singly or with their mates in smaller hammocks. This is socially acceptable as long as the member returns to group sleep, or k'sey nivi, within a short period. As attuned as they are to one another, the Na’vi use sleeping arrangements as an accurate barometer of a clan member’s emotional health; if a Na'vi is seen to sleep outside the group (sumin'sey hulleh), for an extended period, it is generally considered a sign that the clan member is in some kind of distress.
Because of the fine craftsmanship, hammocks can last for more than twenty Earth years. It us up to family elders to decide when a new hammock is needed. Construction takes place over a period of months and generates a good deal of enthusiasm within both the family and the clan as a whole; everyone contributes to the effort. A great deal of time is spent in gathering the correct materials, and it is during this process that most the familial bonding takes place. The construction itself is a relatively informal and straightforward process.
As the hammock nears completion, several ceremonies take place to honor and acknowledge the hard work. When the new hammock is finally installed and the old one is removed, there is a ceremony in which the old hammock is burned on a pyre in a serious, respectful manner. At the end of this ceremony, the family puts on a celebration with food and dance in honor of the moment of renewal.