Eternal Repose is the quasi-sleep-like state that many spirits and undead (not animations) must rely on to reconstitute themselves and/or to compose their sanity against the bleak existence they are in.
This limbo state is a reflection of physical life in a mental howling emptiness where memories and feelings roar by in a flood which cannot be grasped, and afterwards the entity is left in a painful silence. There is no internal monologue, no dreaming. There is no sound or vision unless it is direct burning thought regarding an issue or situation that vexes the entity. No musings and little to none artistic creativity – just cunning. This creates a feeling of profound emptiness and disconnectedness. A feeling of being utterly alone, no feeling of friendship or even equity. In this, rest is a disconnect, just like for the living. During this rest, the entity often surrounds themselves with material items and substances from their living, material life to distract themselves and focus on or just achieve a fleeting level of comfort and safety with. In this, they sometimes have a waking dream-like state that is the only semblance of life and these ‘dreams’ are not remembered (they shuffle through their consciousness like a slideshow), but like the living, aid in retaining sanity. It is the equivalent of sleep, and in a parody of or just reflective of old behavior, often mirrors the time they would spend when they were alive and vital. While in this rest, they can awaken instantly – consider it a Light Sleep at worst, a conscious torpor. If they don’t pursue this rest, they lose their sanity; In some senses, it is more critical than for the living.