Has anyone heard of cyclical vomiting syndrome?

My almost six year old vomits randomly for hours and then sudden it’s gone. This was happening about every four weeks or so last year. The dr gave us anti nausea meds, heart burn meds, and a diagnosis of CVS (cyclical vomiting syndrome). My son went to a gastrointestinal specialist who said that this happens with kids but that there was nothing wrong internally.

He has no fever

He’s not dizzy

No diarrhea

No headache

But he can’t hold anything down. If he literally has a sip of juice, water, etc about 15 mind later he violently throws up - like loudly and forcefully.

I don’t feel right about this diagnosis - I’ve never heard of it. I can’t find a lot online about it. And I’m still not sure what causes these rounds of vomiting.

Any insight suggestions feedback would be appreciated