The mind and body are not separate from one another as we like to think; people who have had heart problems often have to take anti-depressants for depression caused by their heart problems. As Shezbut says, there are physical problems that mimic some schizophrenic symptoms and/or could cause them (the symptoms, not schizophrenia). "All in your head" is not a dirty phrase, it just means the doctors do not know how to help at this time.