1. PTSD is in actuality frequently triggered by a single, discrete, traumatic event. 2. The feelings of ostracization/alienation and general disengagement from social discourse are indeed well known markers -- except, they follow, rather than lead the onset of PTSD. In other words, they manifest as a result of PTSD -- not the other way around.

Source: https://www.psychiatry.org/patients-families/ptsd/what-is-pt...