i had a huge Lab/Shepard mix that started having "grand mal" seizures at 3 yrs of age, which are the worst kind!
He would have bouts that came and went all night at times, was out of it between them and paced the floor constantly, would walk into a corner and didn't know how to get out of it he was so messed up...
Took him to the University of Missouri Vet school at the vets recommendation, after a lot of trial and error we had to mix "phenobarbital pills" with "potassium bromide", and when he had one give him 20mg of valium, but the seizures went from every month or two to once every 18 months...that's a worst case scenario.
Had another lab that had minor seizures, the vet gave him some phenobarbital pills and she was fine after that,,,
If the legs are just moving it is a minor seizure, you would know if it was a grand mal believe that, the whole body seizes, they pee, and their mouth chomps uncontrolably and they even squeal at times...probably just needs some phenobarb and will be fine!
OH Yeah, never pick up a dog having a seizure, talk to them so they can hear you when they start coming out of it and only do that after you clear the area they are in so they don't get hurt...I've been through 100's of them LOL