My DS has done this several times. after the first "pass out" I learned quickly how to recognize it and "snap" him out of it - usually a little poke in the ribs, I've heard blowing in the face works too.
Our PEd wasn't concerned either, said it's fairly common, although frightening (she said some kids have done it in the car while the parent was driving...that would be scary!)
anything can trigger it - a big "boo boo", or something else very upsetting that causes that really intense cry.....then hold breath.....then still holding breath....then still holding breath......
He's just over 20 months now, and hasn't passed out or come close in a while now - he seems to remember to breath when he's really upset now.
I don't have any links to anything... sorry
Glad to hear you little guy is better
