Post traumatic stress disorder is usually understood to be the result of some kind of acute trauma. The classic stereotype is the returned soldier who woke up in the wreckage of a Humvee after an IED blew parts of him and most of his best friend away, and thereafter cannot stand fireworks, or a backfiring car.
There is a more subtle version of it that has recently been identified. Complex PTSD is the result of a cumulative and ongoing trauma, usually in the context of an long term situation. Childhood sexual, emotional and/or physical abuse, long term caregiving to someone mentally or physically ill, kidnapping or entrapment and other forms of inescapable similar circumstances can and do produce PTSD.
It often intensifies and becomes full-blown either in the context of a similar trauma (the straw that broke the camel's back) or even when the person is removed from the traumatic situation and their life gets better, which gives the sufferer enough respite for their feelings to catch up.
Depression is a common symptom, and so are constant ambient feelings of dread and hopelessness. They can withdraw emotionally from others and frequently see themselves as useless and unlovable.
The behaviors that manifest are wide-ranging, anything from seeking approval from others by becoming a "fixer" or counsellor/helper of some kind, to violent outbursts and withdrawal from others. They may become "doormats" (seeking out partners who can never be pleased) or substance abusers, relying on a co-dependent relationship with someone or something - or become control freaks in their relationships. They frequently have catastrophic thinking patterns, always fearing the worst, and showing a heightened vigilance towards events in their lives. It can also manifest as learned hopelessness.
Low self-esteem and self-hatred are also common.
Very little has been done in terms of research into treatment, or even the type and/or extent of neurological damage done by this condition. But the recommendation is just about the same as any other kind of stress disorder: looking after yourself, getting therapy, journalling and so forth. It is not in the DSM as such, though the first publication on the topic was Judith Herman's 1992 book "Trauma and Recovery". It is usually coded by the ICD as (31.1), which is "personality change due to classifications found elsewhere".
It is not to be confused with CTSD - continuous post traumatic stress disorder, which was first identified in South Africa. This is caused by repeated exposure to high levels of violence, seen in populations in which there is a series of civil conflicts or other religious or political persecutions.