i think everyone spaces out, ptsd or not. pressure of things to do, ie to much on your plate or a single thought that just never got the attention it deserved. inability to concentrate and getting bored will also cause us to float away mentally.

i am no expert however i do know by observation of others. how many people draw a blank? i believe everyone does at some point in time.

i think the real difference is when a trigger occurs that cause us to pay attention to some noise, something dangerous might happen. i think we believe we space out but instead we are fultra ocused on our senses to keep guard. if you have ever been "in the zone" while playing sports you would realize afterwards as you are waking, that there were no words in your head, all was visual. i think "spacing out" allows senses to get 100% just as we were in a zone.