The paper gives a theoretical justification of CNS abnormality developing in patients who have a history of critical and terminal states, including clinical death. The most significant abnormality is that which is termed posthypoxic and/or postresuscitation encephalopathies whose nature has not been elucidated particularly at the cellular and molecular levels. It is emphasized that this involves brain abnormalities, which is a sequela of hypoxia or ischemia of systemic origin, rather than primary brain damages. In some patients who have sustained a severe hypoxic episode of any nature and recovered their psychoneurological status ever rapidly and rather fully, there may be an abrupt progressive deterioration of their neurological status in some days or months, which results in death or grave irreversible disability. It is concluded that not only do reparative and compensatory processes occur, but also there are phenomena of progressive degenerative changes in a primarily successfully resuscitated person or experimental animal in the central nervous system in the postresuscitation period. A classification of psychoneurological disorders in patients in the early postresuscitation period has been made and ways of their prevention or alleviation have been indicated.