[ He listens quietly, letting a small bit of silence stretch before responding. ]
It sounds like he's suffering from post traumatic stress disorder. It's commonly connected with soldiers, but anyone who experiences a traumatic event can suffer from it. Natural disasters, accidents, death, sexual or physical abuse or even neglect can result in PTSD. It's a form of anxiety disorder.
Has he had difficulties concentrating or sleeping lately? Any panic attacks? Change in activities?