My Budgie Limps

Hello! I noticed yesterday that my budgie is limping. There's no swelling, no irritation, no lumps or anything of that nature. No visible signs of injury. If fact, she's pretty happy and as active as always. Read as many articles as I could. Some say that it can be a simple sprain. Question: when do I need to start panicking? There's a vet hospital near by, by I don't want to stress her out unnecessarily and it's freezing cold outside now.