S.L.
L.,
I suspect that what you might be dealing with is breath holding. My oldest daughter sent me screaming to the ER the first time when she was about 11 months old. She was crying and then nothing was coming out of her mouth. She passed out, eyes rolled up in her head and she went limp. After that she was breathing, but exhausted for hours. They told me in the hospital that breath holding comes on for some children when they become upset. If they start to cry but immediately stop breathing, they are not clamping their mouth shut and puffing out their cheeks like some cartoon of a spoiled baby holding their breath on purpose!
One time when it happened my father in law was nearest to her. He flipped her over and held her upside down and blew straight in her mouth. It startled her into breathing again. After that, I tried to do the same. There was almost never any warning at all. The good news is that today she is 24 and a half years old and she's healthy as a horse. These little incidents only happened once or twice per month. They always scared me. She grew out of them by the time she was 3 or so.
You still need to have him checked out and I would buy a monitor that goes off when he sleeps if he stops breathing. They make them that are not too expensive anymore.
Suzi