A 50-year-old man with small-bowel fistula has been receiving TPN for the previous 3 weeks through a single-lumen central venous catheter. He is scheduled for exploratory laparotomy and closure of fistula. On the morning of the day of surgery, TPN is discontinued and intra-venous infusion with balanced salt solution (Ringer's lactate) is staed. An hour later, the patient is found to be anxious, sweating, and tachycardic. What is the most likely cause?
Anxiety Hypoglycemia Hypovolemia Unexplained hemorrhage