Vasovagal syncope is mediated by the autonomic nervous system. Some people with dysautonomia (disorders of the autonomic nervous system) do have gastrointestinal issues as well. The autonomic nervous system controls digestion, so as Jaynes1 pointed out, gastroparesis can occur if there is significant disorder of the ANS. I believe an isolated episode of vasovagal syncope is classified differently than recurrent syncope, and most likely not viewed as indicative of ANS disorder. Still, you may want to post this question in the Dysautonomia community in case any of the members there have insight. It can't hurt to ask.