A 32-year-old man with ulcerative colitis (UC) and a body mass index (BMI) of 15 kg/m² has been admitted for toxic megacolon to the intensive care unit for 4 days. He was treated for septic shock and was on pressors for the first 48 hours. In the past 2 days, his condition has significantly improved, and he is off vasopressors and having 5–6 bloody bowel movements daily. Patient has been kept NPO in the ICU and is now being transferred to the floor. He is afebrile and hemodynamically stable. His white blood cell count continues to improve, and he has started on enteral feeds after 10 days of NPO status. After he is started on enteral feeding, he develops double vision, disorientation, and dyspnea. Which of the following is the most likely the cause of his symptoms?