 Unfortunately, depression is a common symptom found in patients with schizophrenia and can fly under the radar for years before others become aware of its presence in a patient.However, very little research has been done on the subject, meaning there are few answers to how it should be systematically diagnosed, treated, or what course the illness will take.Some scientists would entirely deny the existence of post-schizophrenic depression, insisting it is a phase in schizophrenia as a whole.