According to your description of his condition (“dizzy spells, chest pains, trouble breathing, lost consciousness”) and his medical history (congenital atrial fibrillation, Hodgkin lymphoma-stage III, recent chemotherapy treatment…), it seems likely that your boyfriend is experiencing decompensate heart failure. This type of heart failure is probably due to the advanced Hodgkin lymphoma and recent chemotherapy rather than atrial fibrillation. If the tumor responds to the chemotherapeutic treatment and if your boyfriend overcomes the side effects from the chemotherapy, he may recover from the condition.