I have a 65 year old male patient who has episodes of nocturnal vomiting. Initally this happened every 90 days. It has now become more frequent. He has had a colonoscopy in March 2010. They found a large polyp at the rectum which was large and had to be removed surgically in fall 2011 and it was negative. He was tested for H. pylori last fall and that was also negative. He had a negative stress fall 2011 and it was negative. What could be some of the causes?