This was a thought I had at 2am last night. Do you suppose it's possible for dogs to have some kind of mental handicap? People can, why not dogs? I know they can suffer from disorders like anxiety and OCD so do you think it's possible? Discuss 
If I miss his walk he'll stand by the door. If I miss "cuddle time" he stands on the couch
With regards to the weaving, I have seen some horses that it was just boredom and others that would be turned out to hundreds of acres of pasture with lush grass at the fence and still weave. So I agree, a lot of behaviors can be breed traits or training or management issues, but I think sometimes animals can have true mental issues.An example - a horse weaves in his stall. Does he have OCD or does he just need more stimulation in the form of turnout with pasturemates? Often the latter would solve the problem.