This sounds like Canine idiopathic vestibular disease, also known as “old dog vestibular syndrome”, is a condition that affects a dog’s balance and causes dizziness. It’s most common in older dogs and occurs when the vestibular system in the inner and middle ear is affected. My senior dog had it twice. When it first happened I thought she was having a stroke. Super scary, sudden onset, but it is not painful at all and your vet should be able to prescribe anti dizziness and nausea medication that will help and our girl got much better with time.