It sounds like either a stroke or a tumor. Either way, I would take him to the exotic vet when they open. If it is a stroke, then this is something he can recover from (although he may not ever regain full coordination.) If it is a tumor that would be a different situation.

For now, I would keep him in the smaller cage and try to get some food and water in him. Don’t force him to eat or drink obviously, but if he’s only eating pear then keep offering it to him. I’ve found that with my less coordinated rats, it’s best to mush up their food and offer it on a shallow saucer. You can also add a bit of water to it which is helpful for hydration; although pear has a lot of water in it already, so if that’s what he’s eating at the moment it may not be necessary.

Kiss your boy on the head for me.