esrblog thinks it's gas, because it changes over time and he gets relief from burping, but his MD thinks it's some kind of virus or other infection causing gastric distress.

While he was recovering, he noticed that his colon had been in spasm (which he noticed only when it began to relax and he developed a brief case of the runs).

However, he doesn't get a migraine or other headache with it; just the abdominal pain and nausea/vomiting. His BP when they monitored at the hospital was elevated but not shockingly high. Thanks for the info, though.