Hiccups are unexpected, spontaneous tightening of the diaphragm muscle. As the muscle contracts or tightened frequently, the gap between vocal cords snaps close to make sure the inflow of air and creates the hiccup sound. Irritations of the nerves that expand from the neck to the chest are mainly responsible for hiccups.
Even though hiccups are linked with a variety of disease like, it can be cause because of serious disease like pneumonia or may be hiccups come because of some destructive stuff builds up in the blood, but in general hiccups are not serious and have no accurate reason of happening. The diaphragm approximately works flawlessly. When you breathe in, it pulls down to help pull air into the lungs. When you breathe out, it pushes up to help push air out of the lungs. But occasionally the diaphragms get irritated. When this occurs, it pulls down in a jumpy way, which makes you suck air into your throat unexpectedly. When the air speedily in, it hits voice box and left with a big hiccup.
Mainly diaphragm is irritated, when someone eats too quickly or excessively, or due to problem in the stomach or the throat, or when someone feeling nervous or thrilled. Almost in every case hiccups last only a few minutes. Sometime hiccups can last for days or weeks, but this is extremely unusual and it's generally a sign of some other medical problem.