My 3 year old daughter sometimes cries so hard and long that she stops breathing for a few seconds. She usually does it when she is having a little tantrum, but it has also happened after hurting herself. She sobs and sobs, and then comes a long series of sobs with all the air going out until she can't make noise any more, but the sobbing continues soundlessly with the throat closed until the color starts to drain from her face and she goes limp on the floor, and I am waiting for her to take a breath while telling her, "Breathe. Breathe!" Finally she takes a breath and cries some more, but it's a different kind of crying now. It seems to me more like freaking out because she couldn't breathe. A couple of times I have slapped her face to get her to gasp; it can be a scary couple of seconds. My mother-in-law thinks my daughter does all this on purpose to be manipulative, but I am not sure. How much of this kind of hysterical crying is voluntary, and what is the best response when this happens? Better yet, can this be prevented?