There are a lot of reasons why cats will sleep in the litter box. * Kidney problems: an adult cat sleeping in the litter box can indicate urinary infection or crystal formation in urine that can cause intestinal discomfort or make it very painful to eliminate wastes. * Dementia * If it's a kitten and newly adopted because it finds it cozy and secure. * Multiple cat homes may have some dominant cats marking their territory by sleeping inside their litter boxes. * Stress: if there are major changes in the surroundings, the cats may sleep in the litter boxes to derive comfort. * Labour: when cats give birth, they usually take refuge in their litter boxes. They provide them a private place.