Poor you, it is scary, particularly the 1st one you see 
DS1 has what I think are RASs.
Always in response to pain / shock.
He had his 1st at 8 mo when he toppled over face first onto a tiled floor and split his lip, I was terrified and it seemed like he held his breath forever. In reality it was probably less than 10 secs, but his eyes rolled back and he went very pale and clammy.
I took him to GP who said it was fairly common and he would grow out of them.
He's 3.7 now and had his last one a few months ago.
I think he's probably had about 10 in total over the years and I still find them horrible to see, even though I know they aren't harmful and that he recovers quickly.
I warned nursery about them when he started there aged 14 mo and they weren't concerned as they have dealt with children who have had them before.
Am hoping he'll have grown out of them by Sept when he starts school but presume that if he does have one they will be au fait too.
I read a bit too and was interested about the low vagal tone theory as I was a bit 'fainty' in response to injury / squeamish situations as a child / teenager and wonder if there is a genetic component.
Hope your DS grows out of it quickly 