What Causes Diaphoresis, Vomiting And Tachycardia After Mitral Valve Repair?

My husband had mitral valve repair nearly 12months ago, shortly after the repair he suffered an episode which seen him collapse on the floor with diaphoresis, vomiting, dizziness and tachycardia. Since this episode he has suffered frequent significant bouts of dizziness where he feels dizzy, faint and feels like he is going to collapse. He is having trouble coping with daily living because of these episodes. His cardiologist as sent him for tests with a neurologist to check for a TIA, the test produced no results. We need answers as it is affecting his life dramatically. The repair has been checked 6 months ago and there is now a very mild leak again. His cardiologist seems complacent about the attacks he is having and gives him no answers