I Vomit Out Of The Blue Without Warning, No Nausea,

I vomit out of the blue without warning, no nausea, no heartburn. Endoscopy nl. Before I vomit I get tunnel like vision (only warning) and after I am extremely fatigued and sleep. If not my stomach, what else could be causing this? It's been going on for over a year and is affecting school (have to leave class and nap in car after) I vomited on a customer this. Help