There is no clear or exact reason why we get them. Although they believe its because of the irritation of the nerves from neck area to the chest. This then would cause an involuntary and regular contraction of the diaphragm, simultaneously the vocal cord opening snaps shut causing the hiccup sound.
Irritation of the nerves is multifactorial. Most of the time, it is associated to drinking and eating.
Holding ones breath causes CO2 build-up (as in drinking a glass of water). This stimulates the vagus nerve that would stop the hiccups. OR SO EMEDICINE says. hehe.
Haay, it seems really boring to answer these stuff.
