Two years?! Then what does your doctor think is the issue? I don't think an endocrinologist would tell you different. I also had Graves. I had thyroid ablation in 2003. Do you always get T3 T4 and TSH panel? You don't mention other symptoms: insomnia; wired/tired feeling; muscle weakness or soreness - especially in quads; hair loss or thinning issues; sensitivity to heat; weight loss? First glance, it doesn't sound like overdose to me. TSH is always in normal range? I would look to other issues. First, are you drinking enough fluid? Fruits, vegetables? No other overindulgence of caffeine or sugar (chocolate, tea) which can jack you up? Might be something as simple as electrolyte imbalance. Or anxiety. Did your primary suggest cardio referral? That would be my first go2. Lightheaded and dizzy doesn't compute with euthyroid. FYI: I take Synthroid because it has less variance. I assume you know never to self-adjust and wait 6 weeks for testing after doctor recommended dose change.