This article is from the Epilepsy FAQ, by Andrew Patrick (andrew@calvin.dgbt.doc.ca) with numerous contributions by others.
It is possible that some dogs are able to detect pre-seizure changes in
the physiology of some people with Epilepsy before the person becomes
aware of them. In many cases, the person with Epilepsy is aware of an
aura before the onset of the main part of the seizure.
Not enough is known about how dogs can detect seizures before their
onset to know exactly what sense(s) are involved in this detection.
However, one might hypothesize that since dogs can detect chemical
changes due to fear, seizures that are preceded by a sense of fear
might also produce detectable changes.
 
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