Dog arching back and unstable

Curious if anyone's run into this before. It's happened a few times over the last few months, including earlier today. Our dog suddenly seems to lose coordination in his back legs, and will stumble over to whoever is closest to him. Sometimes he'll arch his back like he's about to poop. Doesn't seem to lose consciousness at all.

When it happened tonight I took him out and he went the bathroom right away (case of diarrhea). One he came back in he was back to his normal self.

We've talked to the vet and they said it doesn't sound like a seizure, and just to keep an eye on him. Not sure if it's related, but we've been treating him for a ruptured anal gland the last week and a half.

Any thoughts?

Ruptured anal gland is probably the problem, spasm or pain when he needs to go toilet. Talk to your vet about pain relief and monitor him closely poor babe.

It's because your dog's in pain most likely due to the ruptured anal gland. An arched (roached) back and being unstable on the back legs is quite common in Shar-Pei when they're having and FSF attack, a disease peculiar to the breed.

As has been advised I'd speak to your vet about pain medication.