A patient of schizophrenia on neuroleptics, his psychotic symptoms get relieved but developed sadness, talks less to others, remain on the bed, all of following are likely causes except -

In post-schizophrenic depression, the depressive symptoms become florid as an outcome of schizophrenic illness and not as a reaction to it. Schizophrenia resolves to a great extent but some symptoms still persist. For diagnosis, there should be a positive history of schizophrenia within the previous year. If schizophrenic symptoms are not present, a depressive episode is to be considered. Differential diagnosis of post-schizophrenic depression includes residual phase (negative symptoms) of schizophrenia, Schizoaffective disorder (Depressive type), adverse effects of antipsychotics (Parkinsonism, akathisia).