It sounds like your girl Annie was experiencing some sort of seizure type event.
Seizures are rhythmic, repetitive muscle movements which the dog is unable to control and often loses consciousness during. Many dogs will repeatedly have chewing motions and can lose urine and stool control. Some dogs don't lose fully consciousness or fall over, but rather become very uncoordinated and are unable to respond normally to stimuli.
There can be several reasons for seizures.
The most common is idiopathic epilepsy. That means that we don't know why but a circuit of sensitive neurons in the brain gets stuck repeatedly firing. Epilepsy begins happening most commonly in dogs 6 months to 6 years of age so she is really too old for this to be the cause of her episode. We do believe that there is a genetic basis for dogs to have epilepsy as certain breeds are more commonly afflicted and siblings will often have them as well.
Other causes for seizures are viral, bacterial, parasitic or fungal infections, toxin exposure, metabolic diseases leading to waste products building up and affecting brain chemistry, low blood sugar, or even granulomas or masses in the brain.
Most of the other disease processes that cause seizures cause other symptoms, those dogs are sick or abnormal other than the seizure. How has she been lately other than her episode? Any changes in appetite or water consumption? Changes in sleeping, or personality? Loss of endurance when exercising?
Some dogs with lower than normal seizure thresholds will seizure in response to being exposed to artificial colors, preservatives or gluten. So you might wish to feed her a diet without artificial dyes or flavors and one that is wheat free. Blue Buffalo purports to produce these sorts of foods.
Decreasing stress is also a way to avoid seizures so if you know an event will be stressful for her avoid it if possible. You can also use calming sprays such as DAP (dog appeasing pheromone) or pheromone impregnated collars to keep her calm.
Exercise should be kept at normal levels. Exercise is a great way to naturally relieve stress and increase positive endorphin levels in the brain.
In a patient with seizures I would have your veterinarian examine her, check a biochemistry profile and urinalysis to look at organ health and a complete blood count. We do want to make sure there are no underlying problems.
If her seizures become more frequent than once a month or more than one happens in a day, even if it has been several months since the last one, I would discuss medication to prevent them. The reason for that is the likelihood of status epilepticus (one seizure after another) and possible brain damage is higher with those scenarios and we wish to avoid that.
If her episodes were more of a fainting or syncope episode (where she just seemed to collapse and lose consciousness rather than rhythmic muscle movements) then she may have a heart condition. Your veterinarian can also examine her for any heart rhythm abnormalities and recommend medication to help.
Please let me know if you have any further questions.