An unrested soul is the soul of a person or an animal that, for some reason, remains in the Middle World and lives among the living.
There are many causes and many signs. The most common cause is an unfinished term on Earth. In other words, the person left earlier than they were meant to.
People often say that a person lives exactly as long as fate has allotted. This is not always true. A human being is fragile. People make mistakes, leave the right path, take their own lives, develop chronic and inherited illnesses, work in harmful conditions, destroy the body with alcohol and other habits, receive pollution and punishment from the world of spirits. There are also murders, accidents, disasters, and wars. All of these can cut a life short and change a destiny.
In some cases of sudden death, the soul does not understand that death has already happened. It continues to live as if it were still a living person, and cannot understand why people no longer notice it. When life ends in this way, the soul may remain in the Middle World. It suffers, wanders, and without meaning to, disturbs relatives, loved ones, and even complete strangers.
After death the soul finds the road to the Lower World and, after some time, reaches the gates of the realm of the dead. If the earthly term is not finished, the soul is not allowed through and cannot come to divine judgment. Then a hard choice appears: return to the living, or wait by the gates until the term is complete. Most such souls were used to comfort in life and do not stay by the gates. They go back to people. They continue to live in their homes, stay in their cars, come to their relatives. In other words, after death they try to keep living the familiar life among the living.
In shamanic practice there are also cases when a living person themselves calls an unrested soul and binds it. Sometimes this happens without intention, sometimes by desire. It happens when a person cannot let the deceased go: keeps talking to them, remembers them constantly, weeps, calls them for help, asks them to come in dreams, visits the grave too often. Or, on the contrary, the soul itself does not want to leave.
Unrested souls are not rare in the modern world. They appear quite often in shamanic work. Not every shaman can diagnose them. This requires experience, access, knowledge, and strength.