Post traumatic stress syndrome is due to -

REACTION TO STRESS AND ADJUSTMENT DISORDERS This category in ICD-10 consists of disorders which are temporally related to an exceptionally stressful life event ( acute stress reaction and post-traumatic stress disorder) or a significant life change (adjustment disorders) immediately before the onset of illness. Ref: A Sho Textbook of Psychiatry, Niraj Ahuja, 7th Edition, pg. no.111