A 48-year-old woman from Bangalore with type 2 diabetes mellitus for 8 years is on metformin 1000 mg twice daily and gliclazide 80 mg once daily. Her HbA1c is 7.8%, fasting glucose 118 mg/dL. She reports occasional episodes of sweating, palpitations, and tremor in the afternoon (3–4 hours after lunch), which resolve after eating a snack. Her BMI is 26 kg/m², blood pressure 128/82 mmHg, and renal function is normal. What is the most likely cause of her symptoms, and what is the most appropriate modification to her current regimen?