Sudden vomiting mostly after physical stress or in the morning?!

Hello i am a 17 year old guy, for the last 3-4 years ive had sudden vomiting without nausea about twice a month, what are the most common causes of this ? it mostly happens in the morning or when i worked a ground exercises and stand up, its not like normal vomiting that keeps going, this is like 1 vomit and then i am completely normal again, as a reflex it usualy gets instantly swallowed before it gets up .... witch is rly disgusting .... any clue what this could be ?