It is not unusual for a dog to vomit prior to a seizure. A friend of mine's PBGV always vomits prior to a seizure. I have heard of others say that they use that as a sign a seizure is coming. Vomiting does not cause the seizure. Those that live with a dog with seizures that happen more frequently keep a log to write down all things that lead up to the seizure so they can track the frequency and if there are signs to watch for.
Julia
We have a younger lab, siezures started at 2, she will vomit before every siezure. We are always on alert if she vomits. Every one is a grand mal...they last about a minute, minute and a half and then she comes out of it. Everything back to normal within 10-15 minues. No medical reason for doing it other than hereditary epilepsy. We are lucky she only siezes several times a year.
Thank you for all the input. This is only our second seizure, a year apart between them. It has to be the scariest thing to watch. You feel so helpless while it is happens.