What's up with this squirrel (video)?

Video.

Unfortunately I didn’t manage to tape the most extreme examples of the behavior, but it’s happening about 3 seconds in. He stops what he’s doing and starts tipping over.

I taped it because this is the second time that I noticed a squirrel doing this in my yard. Is this just something squirrels do, or do you think this is the same one as before?

Is he sick? Just a quirk? Drunk? xD It just struck me as funny.