Beagles, Dachshunds, Labs and Golden Retrievers are very commonly affected and these are among the most popular breeds around. And after that Beagle won Westminster this year, you can bet that Beagles will get even more popular.
It's important to differentiate true epilepsy from all the other potential causes of seizures.
Seizures can occur secondary to a host of medical and metabolic conditions and, as such, are considered to be intra cranial (brain) and extra cranial (everything else) in origin. Seizures due to epilepsy or to something like a brain tumor are intra cranial in origin while a seizure from ingestion of a toxin or something metabolic like hypoglycemia (low blood sugar) are from extra cranial causes.
True epilepsy is often diagnosed by history and eliminating all the other medical and metabolic causes of seizure activity. Since we don't know exactly what causes the abnormal neuronal activity in the brain that results in the seizures themselves, epilepsy is said to be idiopathic in nature. Idiopathic is one of my favorite medical terms. It saves doctors from saying something like "we don't have the foggiest idea what is going on here".
Epileptic seizures are most commonly generalized, what we used to call grand mal, as opposed to focal or in the old vernacular, petit mal. By the way, grand mal and petit mal are French, meaning literally, big sick and small sick. Generalized seizures are the classic form where the dog loses consciousness and may fall on their sides paddling their legs.
Focal seizures can involve small muscle groups and the dog may not lose consciousness at all. In either case they may be disoriented preceding and immediately after the events. The seizure itself is called the ictal phase and the aftermath is called the post-ictal phase. Between seizures, or in the interictal phase, most epileptic dogs are completely normal. Being totally normal between seizures is diagnostic for idiopathic epilepsy.
In really bad cases where the seizure is ongoing (status epilepticus) or if the seizures repeat with very short interictal phases, emergency treatment is called for. In most cases owners see only occasional seizures and miss others.
The goal of treatment in most cases is to reduce the frequency and severity of seizure activity so the dog and family can live a reasonably normal life. Daily medication is usually reserved for seizures that occur at least once per month or occur repeatedly in a brief period of time or are increasing in both frequency and severity.
There are many different anti seizure medications available. Most commonly veterinarians will use either phenobarbital or potassium bromide. You will have to work with your veterinarian to get the dosage of phenobarb working well for your dog. The goal is to achieve a relatively constant blood level that will control the seizure while minimizing the side effects of phenobarbital. Slight sedation is the most common side effect, but accurate dosing can minimize this while providing relief from symptoms.
I've known lots of dogs and even some people who have lived long and otherwise healthy lives with epilepsy. No doubt you know someone with epilepsy that has the disease so well controlled that you wouldn't even know they are affected. That can certainly be the case with dogs too.