Hello Adam and Thank You for contacting JustAnswer
I believe what you are seeing is a condition called Old dog vestibular disease.
The vestibular system is responsible for keeping the head and body in the correct position and tells the brain if we are standing, sitting, lying down, falling, spinning in circles, and keeps the body balanced.
The most common cause of this is a problem in the inner ear, however in an older dog often the actual cause is not known.This comes on so suddenly that often owners think their dog has suffered a stroke.
In most cases this will resolve on its own but can take as long as two weeks. Often dogs are hospitalized only for supportive care as the dizziness often causes vomiting and lack of eating and drinking.
Here is more in depth information on this condition
I would suggest having her seen by your vet to see if a cause can be found and if treatment is needed.
Until you can have her seen medication used to treat human motion sickness is often helpful, Dramamine is the recommended over the counter medication.
Here is information on the use of this medication
I hope this has been helpful and she recovers soon, please reply back if you have additional questions or concerns
Edited by Candy on 11/2/2010 at 11:19 AM EST