When the Carefree Trait is in effect things get even more out of whack. The times a Tense Moodlet would come up, they end up Angry, or Sad, or some other nonsense that's even farther removed from what they ought to be feeling. That said, since emotions can already overwrite each other in this way, substituting one emotion when another is blocked, it may not be as hard to patch in Fear as some may suppose. It would just add another layer to the hierarchy. During a thunderstorm, they might feel afraid, but if they have a trait that blocks or changes Fear, they might become Tense, then with Carefree, it might sub in something else as it already does.