Douglas does something stupid and injures his wrist or strains his shoulder or something, a la Martin in Ottery, and since it happened in a way that will sound ridiculous when he tells the story, he does one of two things: 1. Makes up a lie
2. Hides it

Something happens that forces him to take some painkillers for it. Only his doctor never told him that complete and utter honesty would be a side effect...