Unfortunately labs are one of several breeds that are more susceptible to epilepsy.
There is often a direct genetic component to epilepsy, but environmental factors should also be considered (especially exposure to toxins such as household cleaners, pesticides, herbicides, formaldehyde in particleboard and new carpeting, etc.).
We have kept retired lab guide dogs in the past, one of which had been retired due to seizures. We currently have a friend who has a working lab guide dog with a history of seizures - the dog was on phenobarb for awhile but became unusable due to side effects (drowsiness, inattentiveness). So the dog was taken off meds and put on a low-toxicity, high fiber diet instead, which helped quite a bit except for the inconvenience of too-frequent bowel movements, which in a guide dog is not desirable. They also suspected a connection between the dog's seizures and the annual spraying of the apartment complex for roaches, as well as the laying of new carpet in the complex, so my friend eventually moved out of the apartment and into a house. The seizures became much less frequent, but still occurred every few months or so. Fortunately they found a new vet who was sharp and discovered that the dog was borderline hypothyroid, which is common in labs and can be a major cause of seizures in dogs. The dog was started on thyroid meds and within 4 months the seizures had vanished. So before you do anything else, make sure your vet does the bloodwork to rule out a thyroid problem! Dogs with liver and kidney problems can also have seizures due to toxin build-up in the blood, so that should be checked also.
This site has a lot of good info:
http://www.canine-epilepsy.com/
