A 45-year-old male undergoing a minor surgical procedure received 30 mL of 2% lidocaine (600 mg) without epinephrine for local anesthesia. Shortly after, he developed symptoms including metallic taste, dizziness, tinnitus, perioral numbness, confusion, and generalized muscle twitching. His weight is 60 kg, and his vital signs are stable. What is the most likely cause of these symptoms?