Worrying about My Dog

At the moment, I'm very much worrying about my dog Merly's leg. Seemingly out of the blue she started limping, badly. She stumbled a bit yesterday, but there was no limping, so I thought she'd just tripped. Now I'm worried she either did something to herself then or else she stumbled because her leg hurt her. Vet's closed now, we'll see how she's doing tomorrow morning.