have (one's) tail up

To have an optimistic, confident, or happy outlook, mindset, or attitude. We know we have a huge challenge ahead of us, but we have our tails up because of our strong performance so far this season, and we'll do everything in our power to get a win. I know this is a daunting task, so I'm glad you have your tail up—a negative attitude won't help anything. An injury like this has a really long recovery time, so the more she can keep her tail up about everything, the better.