What is a disorder resulting from exposure to a major stressor, with symptoms of anxiety, nightmares, poor sleep, reliving the event, and concentration problems, lasting for more than one month is called?
Most likely Post traumatic stress disorder (PTSD)
The described symptoms sounds very much like PTSD, but could also be something else. Only a doctor or specialist like psychiatrist or psychologist will be able to diagnose for certain.
If the symptoms remain untreated and the situation does not improve, it can lead to additional disorders as well like PTED (post traumatic embitterment disorder), MDD (major depressive disorder), GAD (generalized anxiety disorder), CFS (chronic fatigue syndrome), metabolic syndrome (syndrome X), fibromyalgia, hypertension, etc.
These can in turn lead to physical effects like lethargy, lowered reaction times, breathlessness, sweating, heart beat irregularities, headaches, GIT problems (gastro-intestinal tract), weight issues, muscle and joint pains, etc.