I, too, experienced lightheadedness, often with vertigo, after my septal myectomy at Mayo. To make a long story short, along with the lightheadedness, after two episodes of syncope due to arrhythmias, a pacemaker/defibrillator was installed. I wore a Holter for a month to diagnose this awful condition. My home cardiologist and colleagues well versed in HCM finally figured out what was amiss. Whether surgery or ablation, hearts are undergoing trauma and can show new symptoms down the line. Good luck and wishing you a great outcome!