It is an anxiety disorder. The threat is past so the symptoms "should" not be there. The sufferer is disordered because he is not thinking/feeling like he did before the incident(s) that caused the PTSD to be developed and it is interfering with his normal life. It's not a "crime" or something bad to be diagnosed with PTSD.

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001923/