Dog Dragging back legs

My dog is a cocker spaniel-poodle mix. 4 years old, 25 lbs, male.

4 days ago we saw him dragging his leg getting up from his bed to go and eat. Then after he got up, he looked just fine, he runs, eats go to the bathroom, no pain.
Today it happened again. It seems he is having trouble to get up.
what could be wrong?



Thanks, it sounds like it might be a serious problem - did you take your dog to the Vet and if so how did you get on?