Is it possible for a dog to have a stroke?

My dog is 13 1/2 years old. Lately he's been acting weird. He'll walk in to a room and just stop and stare. Doesn't look around, doesn't do anything, just stands there. When he lays down he'll just plop on the floor in any old position and lay there, sometimes for hours, and never move. This morning when we went for our walk he was all over the place - wobbling, stumbling, tripping over curbs. He walks into things, walk right through his bowl, shoes, newspapers, whatever. He'll stand at the door and face the corner where the hinges are. Is it possible for him to have had a stroke or is this just waht happens when they get old?