My budgie has been bobbing its head a lot, and by A LOT I mean every minute. I read in other places that it is a good sign of friendship and could be humorous, but I don't think this s the case with my bird Tweety (Female). Tweety has also been very sad looking and slouching. It doesn't chirp and sits alone. (We have 3 Other Birds). Is this just a bad habit or should I be worried about a disease or Illness?