Mental illness is actually akin to a physical disease in the brain. It can occur due to genetics, brain structure or extreme trauma or abuse experienced by a person. It usually manifests in two forms – related to mood and anxiety. The latter are more common and are classified as post-traumatic stress disorder (PTSD), obsessive compulsive disorder (OCD), panic disorder (panic attacks), generalized anxiety disorder and specific phobias. Mood disorders, on the other hand, are related to various types of depression.