Disorders of consciousness include those in which the perception of external objects and spatial and temporal orientation are disrupted, thinking is disordered, events are not fixed in the memory, and alienation from the real world sets in. Stupor is frequently encountered, manifested in retardation, somnolence, impoverished psychic life, and elevated threshold for external irritants. Cases range from mild to extremely severe, characterized by sopor and coma. Delirium may also result, characterized by illusions, hallucinations, affective disorders, acute delirium, and motor excitation.