We have a bearded collie cross age approximately 10 years old. Last Friday she was fine all day until about 7.30pm where she started limping (this was her rear left leg). She didn't seem to be in much pain (no whimpering etc).
She slowly improved on Saturday, putting the leg down every few minutes and by Sunday she was back to normal.
Hwoever, it has all started again now. She is limping and again seems happy enough except for the fact that she won't put the paw down.
She may have picked up something in her foot . Have a good feel round her foot and see if she whimpers at any certain point. But I would certainly take her to vets if it persists.
Sounds like a touch of arthritis, try her on some glucosamine supplement or Denes Greenleaf, and you could get her a Biolflow collar. I'd check with the vet first in case she has done something like damage a cruciate ligament, but the intermittent lameness would indicate arthritis more likely. Probably worse when the weather is damp, like my shoulder!