Aauugghh. I wish they could all stay 5 years old. One morning last week, we woke up and Chelsea, the chow, couldn't walk. She had a severe head tilt and her eyes were darting back and forth. So I panicked thinking it was a seizure or a stroke and rushed her to the vet. The vet said it wasn't serious - a disease of old age. Chelsea is 13 years old. It's called Canine Peripheral Vestibular Syndrome and is treated by using a motion sickness medicine.
I'm very thankful that it wasn't something worse. It was really hard for us to see her unable to walk and when she tried, she would fall down or go in a circle. There is a good website that describes this problem...
Canine Peripheral Vestibular Syndrome
A week later, she's doing better and with the help of over-the-counter motion sickness medicine she has compensated and is able to walk in a semi-straight line. She's not as stable as she used to be, but she is very much improved.