One of the potential adverse reactions to vaccinations is seizures -- has your dog recently been vaccinated? Rabies vaccines are associated with adverse neurological side affects.
Significant calcium deficiency can cause seizure-like episodes, have you had a blood test to check calcium and phosphorous levels? High phosphorous foods (meat, eggs, nuts) bind with calcium, as do high oxalate foods (oatmeal) and may deplete your dog's levels to a point where it will cause problems. Poison will also cause seizures.
You might want to do an online search for "canine hypocalcemia" or just "hypocalcemia". The Lowchensaustralia website will take you to an article on this subject in which it states that the signs of low calcium levels (hyocalcemia) are: "Muscle tremors, restlessness, panting, incoordination, grand mal seizures and fever as high as 106."
Further, the above articles thats a one of the possible causes: Poor Nutrition - "Home brewed" diets usually are at fault. The owner innocently may be adding too much unbalanced meat to the bitch's diet, thinking the extra protein is beneficial. What's really happening is the calcium to phosphorus ratio is out of balance because the amount of useful calcium in the food is actually reduced! The ideal contains a ratio of calcium to phosphorus of 1.2 to 1. (Many organ meats such as liver have a ratio of calcium to phosphorus of 1 to 15!! Liver is great for dogs but if it comprises a large part of the diet, the calcium/phosphorus ratio of the diet will be improper.)
If you have chickens or wild turkeys roaming your yard, you should be aware that their droppings are extremely high in phosphorous and can cause a problem if your dog eats too many of them. If the droppings are charging your dog's blood with phosphorous, it's going to drain him/her of calcium in order to maintain proper pH balance and cause muscle twitching, etc...
The British Health Protection Agency states about Phosphorous in their FAQs "It has been used as a rat and rodent poison.."
The PetEducation website owned and operated by veterinarians states under Eclampsia (Puerperal Tetany, Milk Fever, Hypocalcemia) in Dogs "Eclampsia, also called milk fever or puerperal tetany, is an acute, life-threatening disease caused by low blood calcium levels (hypocalcemia) in dogs ...."
One of our dogs developed severe seizures after the second of his puppy rabies shots -- his head shook so hard we thought his eyes would pop out, it was terrifying. After this seizure activity triggered by the vaccine, he became prone to them from other triggers. Whenever he ate too many high phosphorous foods (or chicken droppings), he would seize. Giving him 1/2 a quart of plain organic yogurt would calm his seizures within 15 minutes, when they were food-related.
Personally, I would have a complete blood count done to check for mineral levels if you don't think vaccines or something your dog is eating is causing the seizures. PLUS, I would consult a Homeopathic/Holistic veterinarian for an alternative treatment, you can do an online search for one near you at American Holistic Veterinary Medical Association and Academy of Veterinary Homeopathy.
Combination Vaccines, Multiple Shots--on Page 16 of the 2003 American Animal Hospital Association's Canine Vaccine Guidelines under Immunological Factors Determining Vaccine Safety, it states that: "Although increasing the number of components in a vaccine may be more convenient for the practitioner or owner, the likelihood for adverse effects may increase. Also, interference can occur among the components. Care must be taken not to administer a product containing too many vaccines simultaneously if adverse events are to be avoided and optimal immune responses are sought. "