Not all seizures fit those categories, though. A dog might suddenly go blind and begin walking into walls, a dog can snap at nothing in the air, or suddenly start barking at nothing. Seizures are caused by abnormal electrical activity in the brain. Something just doesn't work right in making a connection, or it works too well, and overloads that portion of the brain. Either way can cause a seizure.
Seizures come from many causes.
Your vet should rule out all of these possibilities when examining your dog after a seizure. Bloodwork can point towards any type of liver or kidney problems, and X-rays will look for obvious signs of brain or other trauma. Your vet may also ask you about bee stings, which can cause a dog to bark frantically for a few moments before collapsing, or even a heart irregularity problem. Dogs can even have anxiety attacks which similarly seem to be a seizure but are not. When your dog has repeating seizures that are not linked to any physical cause, then your vet will look into epilepsy and encephalitis as possibilities.