A patient admitted to the psychiatric hospital and diagnosed with post-traumatic stress disorder (PTSD) asks the nurse what derealization means, as he hears the psychiatrist use that term. The nurse would say which of the following?

“Derealization is an unreality of surroundings.”

“Derealization is the same as hypervigilance.”

“Derealization is a feeling of being detached or as if you are an outside observer.”

“Derealization is a type of therapy used for persons with PTSD.”