Hello and thanks for researching this very important question!
Although Yorkshire Terriers are a breed that can have neuromuscular side effects of Low Blood Sugar (please make sure that he eats regular meals throughout the day), dogs frequently develop a variety seizure disorders.
Some seizure disorders have a cause, such as previous illness (diabetes, kidney or liver failure, hypoglycemia), toxins, tumors or physical injury (like being hit by a car) that has damaged the brain.
Some seizure disorders are what we call "Idiopathic" (sickness without a known cause). Sometimes a dog will have one seizure, and never another. Most dogs with regular, simple epilepsy can be well treated with drugs.
Seizures can be brief (sometimes there is not even loss of consciousness), or prolonged. They can be mild in their appearnace or physically violent. The more vigorous and the more prolonged a seizure is, the more dangerous it is to the brain.
An older pet experiencing a violent seizure, or repeated seizures, is more likely to be harboring a serious health problem, such as cancer, brain hemorrhage, or organ failure.
***Diagnosis can be as simple as running some blood tests, or as complicated as undergoing an MRI to find a tumor or other brain-threatening condition. Your regular veterinarian can help you start looking for an answer.***
Here are some links to other articles about seizures in pet dogs: http://www.canine-epilepsy-guardian-angels.com/CanineEpil.htm
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