What Causes Headache, Eye Pain And Vomiting After Sigmoidoscopy?

My son is 10. He had a sigmoidoscopy less than 48 hours ago. He was fine yesterday, but by afternoon was real congested. Nasal irrigation relieved it. (History of sinus problems) He awoke this morning to severe headach, eye pain, and has vomited bright yellow this morning. (10 years old, 60 lbs.)