Over the last decade a new kind of service animal has emerged. Seizure alert dogs warn people with epilepsy of an oncoming attack minutes—sometimes hours—before it occurs. This allows the person time to take seizure blocking medication, get to a safe place, or call for assistance.
How dogs detect an oncoming seizure in a human is a mystery. Some trainers and researchers think they detect subtle changes in human behavior or scent before an episode occurs. There are no scientific studies, however, to prove these theories. Trainers also believe the behavior is not breed, age or gender specific in dogs.
Seizure alert dogs are born with this remarkable ability.
cats can do this too, as in pkd's son's case, or like this reference I found:
"Oberon was a seizure-alert cat for me... He & I had a special understanding because we both deal(t) with chronic pain (he had arthritis). He would alert me before I had a seizure or migraine aura."..critters are cool (don't eat them)