Hi Thanks for posting your query. The dizzy spells you are experiencing is due to irregular and inadequate blood flow to the brain ( Medically we call it as transient ischemic attack ). This irregular and inadequate blood flow to the brain is happening due to Atrial fibrillation. Your difficulty to walk or exercise is also due to Atrial fibrillation and possibly heart failure also. In that regard I would like to know few more details. 1. What is your present pulse rate ? 2. Are you on any medications for Atrial Fibrillation ? 3. When was your last ECHO scan done and kindly upload the report? If we control your Atrial fibrillation then your dizzy spells and exertional tiredness shall be corrected. Will be looking forward for your reply. Regards.