I have a 5 year old toy poodle. For probably the last month or so, he has been chasing nothing. He's jumping, almost doing back-flips, running into the corner, trying to climb the walls. It's getting worse. He spends probaby up to 3/4 of his day chasing 'nothing'. When I watch him, it looks like he's chasing a bird, it was always above his head, but in the last couple of days, it sometimes looks like he's chasing something on the floor. There is nothing there, we watch him, and try to 'snap him out of it', by calling his name or petting him. We're getting worried about him, it's almost like he's going crazy. I talked to the vet, he said it sounds like a behavioral problem. Any ideas?

Any possibility he has something like a cataract? A floater? A vision problem?

Is it possible that he is chasing either a reflection or a shadow? Some dogs can get obsessed with doing that.

That is what we originally thought it was, but he does it in rooms which are dark, or have no reflection.

Apple tree is right in her suggestions. I would also look into the possibility of dog anxiety, which can be caused by boredom just as much as it can be created by stress or fear. To many dogs, boredom is stressful.