Hi doctor, my 15 months old son used to hold his breath for a long time whenever he was crying.. since childhood, he was used to do this.. one day, he was crying badly and hold his breath for really long time, and we shake him taaki wo thik ho jaye, but he gone unconscious n still hold his breath.. that was very tough time.. but after time he gets normal.. why my son hold his breath while crying for so long time..??? is everything ok..???