A 58-year-old woman with rheumatoid arthritis is scheduled for hip arthroscopy under epidural anesthesia. The anesthesiologist performs epidural catheter placement at L4–L5 without difficulty. After injection of 12 mL of 2% lidocaine with 1:200,000 epinephrine, the patient reports sudden onset of tinnitus, perioral numbness, and tremor. Blood pressure rises to 160/95 mmHg, heart rate increases to 115/min, and the patient appears anxious. What is the most likely diagnosis and the immediate next step?