Now we know the reason: The LA Times reports that Sheen has a hiatal hernia. The intense abdominal pain was a result of that.
According to the Mayo Clinic, a hiatal hernia occurs when "part of your stomach pushes upward through your diaphragm. Your diaphragm normally has a small opening (hiatus) that allows your food tube (esophagus) to pass through on its way to connect to your stomach. The stomach can push up through this opening and cause a hiatal hernia."
Ouch. The condition can cause severe pain. In some cases it requires surgery.
The LA Times reports that "Two and a Half Men" is on hiatus this week and production is scheduled to resume Monday.