My DD1 has done this a few times now - if she really really gets upset about something (has always been when overtired), she cries so hard that she struggles to catch her breath and goes blue in the face for a couple of secs.
She hadn't done it for a while but yesterday she did it for the first time in ages and it felt like the longest few seconds in the world as her eyes actually rolled to the back of her head, it was like she properly lost consciousness for a few secs and then snapped back round.
I asked a Doc about it once but she just said she'd prob grow out of it?? Has anyone experienced the same thing - I'm not sure whether to get another opinion on this as it's so scary :-(