yes ptsd can cause obsessions and fantasies, they vary person to person though. obsession wise most are pretty harmless. you know, checking ur bed for camel spiders before you get in it, things like that. havent seen too many people who have had "fantasies" that lasted for more than a split second, most of the time its when you first wake up and your kinda groggy and you get a "****, still in f*in wherever" thought before you remember you're back home.