My patterdale does this without the vomiting or what appears to be like yours, hers is not a fit its a scotty cramp as diagnosed by the vet, when she goes out and gets over excited she goes into what appears to be like a fit. However once you calm her down she is fine. This is hereditary but she can live with it but you would never breed from her. I hope yours is not a fit but it does sound like it. Hope it all works out in the end for you.