"When U.S. Marine Chris Merkle returned from his last tour of duty in Afghanistan his family was thrilled to have him back.  Interested in  Add as an interest to stay up to date on the latest news video and analysis from ABC News.  Add Interest But for Merkle the welcome home was also accompanied by some dark problems. He couldnt sleep. He was irritable and had anger issues. He would avoid certain stressful situations like driving in traffic. And he would stay on high alert in the classroom.  And then soon theyre like Youre not the same Merkle recalled of what his family told him. They start to notice that youre not really enjoying the parties of our friends. You only get really excited when youre going to visit former Marines and the people you used to hang out with.  Merkle served three tours in Iraq httpabcnews.go.comtopicsnewsiraq.htm and four in Afghanistan. Readjusting to being a civilian was tough he said and he was finding it difficult to function.  There was almost   years of deploying back and forth back and forth  there was this void this monster in the room thats not talked about until finally it came out. It was like You need to see somebody. Something is going on with you.  While Merkle was a patient at the VA he heard of a clinical psychologist named Skip Rizzo at the University of Southern California Institute of Creative Technologies. Merkle was trying traditional oneonone therapy and said that at the time it wasnt really taking that well. He was looking for an alternative and heard about Skips research that used a new and unexpected way to treat posttraumatic stress disorder  with virtual reality.   Finding the Next full episodes will release Tuesdays on ABCNews.com and ABC News mobile apps. The entire series is available now on ABC News apps on Apple TV httpabcnews.go.comtopicsnewstechnologyappletv.htm Roku and Xbox httpabcnews.go.comtopicsentertainmentvideogamesxbox.htm One.  Nearly  million adults suffer from PTSD httpabcnews.go.comtopicslifestylehealthposttraumaticstressdisorder.htm during a given year according to the National Center for PTSD. The condition can occur after someone has been exposed to a significant stressor and often includes symptoms such as avoidance hypervigilance anger issues and mood swings. One common method for treatment is called exposure therapy. The patient recounts their trauma visualizing it in their imagination and narrates it to a clinician. By repeatedly confronting and processing the trauma the brain can start to reduce the level of anxiety httpabcnews.go.comtopicslifestylehealthmentalhealth.htm and response to those memories.  Thats exactly the approach Rizzo uses with virtual reality therapy.  My mission is to drag psychology kicking and screaming into the st century Rizzo said noting that virtual reality offers a unique opportunity for clinicians and clients alike to be immersed in the environment that evokes the original trauma rather than relying on the patients imagination.  Rizzo has created  virtual worlds for patients and clinicians can add custom elements including helicopters clouds smallarms fire and missiles.   The first thing to keep in mind is that we are never going to replicate an exact simulation of what the patient went through Rizzo said. But we really dont need to.  Merkle explained how the virtual reality experience works. Your brain assumes OK this must be where were at and it fills in the blanks. And as youre talking through it you feel like youre physically there.  Each session lasts for about an hour and a half and the patient speaks about their experience with a clinician as they go through the virtual simulation.  For Merkle virtual reality allowed him to start unlocking memories and work through his trauma.  So it really allowed me to open the door and begin my healing process he said. Im still a work in process obviously but Im so far forward leaps and bound beyond where I would have been without virtual reality."