I've seen a lot of comments regarding the tail curl. Most stating it either means hunting or alert. However my dragon sometimes does it when there is no food around, and there is nothing different about his environment that what is normal. However he does seem to do quite a bit of starting at nothing, and it's nearly impossible to break his concentration
The comments (mine included) are based on our observations over time so they aren't all encompassing or a rule by any means. Just what we generally notice. He may just have different habits than what we've seen which is totally fine and worth noting and recording.
The times that they tail curl varies from dragon to dragon. I guess a bit like cats that swish their tail. Some do it more than others and for different reasons.
Worth noting and recording means that what you observe with him in terms of his behavior is worth remembering and commenting on. That's what others are doing as well when we say the antenna tail seems to mean happy and alert and curious that's just what we've seen them do when their tail goes up. If that's not the case with every dragon it's worth noting since we're all still learning about their behavior and communication as we live with them. It's not necessarily bad or a sign of a problem, it's just something different that we can learn from =).