well this certainly deserves a trip to the doctor's office. you can start with your primary care provider (pcp). it may turn out to be nothing but unexpected violent episodes of vomiting shouldn't be ignored when they happen multiple times. many things could cause this including a food intolerance or allergy. it would be best to get the pcp's opinion as to what might be causing this. meanwhile it would help if your son kept a log of what he ate just before vomiting. also it would be useful to know if his bowel movements are regular of if he's frequently constipated. (not that he's going to want to discuss these topics! ) constipation can cause vomiting in some cases. i wish you and your son all the best with this!
3 days ago my 15 year old son had vomited 3 violent episodes. he seemed to recover but he began again yesterday. both times were sudden he said he started to feel naseous and immediately had to vomit. he'd then vomit until he was completely empty sip water until he felt "normal" and then eat crackers. then have another bout of violent vomiting.