Yeah, I almost posted a link to an article from Web MD (2008) that discussed the numbing aspect but it had some things I fundamentally disagreed with (about PTSD). Also it was written with regard to females. The part I agreed with though gender specific (women) was:
"Women who have PTSD are in a state of being numb. They tend to avoid the feelings of general arousal (not sexual, but more what we think of as alertness and vigilance) because it takes them out of their numbness. That is stressful and exhausting.
Arousal (the sexual kind) is required for sexual interest and response, but it is very difficult for women to choose to be aroused since it requires that they not be numb. It can also bring them closer to the memory in the amygdala of feeling afraid. And, it turns out, they are lacking a safety context because during the stressful event, safety was very much in doubt for them. So, staying numb feels like a safer choice and that makes sex out of the question.
In addition to this dynamic, people with PTSD may also have sleep disturbance, medication side effects, chemical dependency and abuse, and other psychiatric conditions that do not easily predispose a person to choose to be sexual. All in all, sexual lack of interest caused by PTSD must be treated with an understanding of the brain structures and neurotransmaitters, the nature of sexual arousal’s similarities to general arousal, and other difficulties that can develop as a result of a traumatizing event." (Source: Modern Love: Sex and Relationships, PTSD and Sexuality from Web MD March 3rd 2008
I am inclined to think that "people" rather than women, would have made a better article. It does address the preference for numbing being safer. But be forewarned if you look it up, I took exception to some aspects of the article.