One important thing to remember is that when someone has PTSD, it often affects people around them as well. Family members and friends may notice that you are jumpier, anxious, depressed or not sleeping well. Also, people with PTSD tend to withdraw from people. Because of these aspects of PTSD, your family probably already knows that something is wrong. Unfortunately, they may not understand what is bothering you or why you seem so different. The fact that people with PTSD withdraw from those who care most about them is particularly problematic because the support that these people can offer to you may be really helpful in overcoming the problems that develop after a trauma. Remember that many of the PTSD symptoms that are bothering you are common reactions to trauma. They do not mean you are somehow to blame.
There is evidence that susceptibility to PTSD is hereditary . Approximately 30% of the variance in PTSD is caused from genetics alone. For twin pairs exposed to combat in Vietnam, having a monozygotic (identical) twin with PTSD was associated with an increased risk of the co-twin's having PTSD compared to twins that were dizygotic (non-identical twins).  There is evidence that those with a genetically smaller hippocampus are more likely to develop PTSD following a traumatic event. Research has also found that PTSD shares many genetic influences common to other psychiatric disorders. Panic and generalized anxiety disorders and PTSD share 60% of the same genetic variance. Alcohol, nicotine, and drug dependence share greater than 40% genetic similarities.