Eustress Deficiency or Eustress Deficiency Cerebral Infraction, as it technically known, is a neuro-disease which places a person's body into a serene comatose state. The person then stays in this state until their nervous system and vital functions shut down and they die from heart failure.
As such, these people are often called "Living Corpses" or "Empty Shells." This disease is a side-effect and the result of a combination of living a stress-free life, excessive mental care treatments and the loss of a personal reason to live. According to Shogo Makishima, it is the leading cause of death in Sibyl Society. However, due to Sibyl's refusal to acknowledge it, it is considered an urban legend.
As such, the only treatment available for patients is to be placed into a specialized mental care facility until the patient's death. Their death is then listed as "heart failure from an unknown cause" on their official death certificate. It is also possible to forcibly induce Eustress Deficiency through an overdose of hue clearing drugs. Heaven's Leap followers use it to obtain a state they call, "Eternal White."