CNN is reporting that it's either Ted Kennedy or Robert Byrd, but they are unsure. We'll keep you posted. Update: ABC now confirms that it was Ted Kennedy, and that he was removed from the room in convulsions. Obama left the room with him to make sure everything was all right, but has now returned. [ABC News]
Update 2: Robert Byrd also had a medical mishap, and also had convulsions and had to be removed in a wheelchair, according to CNN.
Update 3: CNN has revised their report: Byrd was just helped out because he was "distraught." Also, Orrin Hatch saw Kennedy steady himself and give a grin as he was put into the ambulance.