Steve is suffering from Diverticulitis. It is a very painful and potentially deadly large intestinal ailment which stems from a small initial problem which turns into a big one. My mother suffered from it and nearly died. They removed half of her lower intestine and she was not the same afterwards. She had a hard time going anywhere.
Basically, a small piece of food, say a seed or something non-digestible, lodges itself in the large intestine wall and then becomes infected. Sometimes the body can expel the infected item and recover with no ill effects. Other times, the infection simply grows, spreading and eventually ulcerating the intestine wall spilling...it's "contents"...into your lower abdominal cavity. The infection at that point quickly worsens into a life threatening emergency requiring immediate and radical surgery.
Steve was fortunate to have sought medical help when he did...