Due to her lethargy and continued drooling after the episode that you are describing, it is possilbe that she had a seizure (on both occasions) and she is now in what is called the post-ictal phanse.
In a dog of this age, there are a number of different things that can cause seizures. They include:
Hypoglycemia (low blood sugar)--This can be due to a tumor called an insulinoma
Toxins (Lead, moldy walnuts, pesticides)
Bacterial abscesses in the brain
Infectious diseases (Fungal, viral, parasitic)
Vascular accident secondary to kidney failure
Idiopathic Epilepsy (Seizures of unknown cause)
As you can see, the list is quite long. The first step is take your dog in to the veterinarian for a complete physical and neurological examination. The vet will want to run blood and urine laboratory tests to look for signs of low blood sugar, low calcium, kidney disease and liver disease. If all bloodwork appears to be normal, the next step would be an MRI of the skull to look for a tumor or abscess.
If no cause can be found, then it is assumed that idiopathic epilepsy is the problem. This is treated with lifelong medication with an anticonvulsant.
I am attaching a client information handout that I use in my practice concerning seizures in dogs. I hope that you find it useful.Click Here
Let me know if you hav any further questions.