Code for anorexia. You'll often hear people writing about their eating disorders referring to, "And that's when I met Ana." Or, "Ana was my best friend." It's a strange construction, because it anthropomorphizes the eating disorder, personalizes it, makes it seem like an entity in its own right, instead of just an aspect of you. (I don't think this is coincidence. I've talked to plenty of people who felt that way about their eating disorders, with or without the cute nickname.)