Joe is right. Your diaphragm is stretching too far..
Sometimes the diaphragm becomes irritated. When this happens, it pulls down in a jerky way, which makes you suck air into your throat suddenly. When the air rushing in hits your voice box, you're left with a big hiccup.
Some things that irritate the diaphragm are eating too quickly or too much, an irritation in the stomach or the throat, or feeling nervous or excited. Almost all cases of the hiccups last only a few minutes. Some cases of the hiccups can last for days or weeks, but this is very unusual and it's usually a sign of another medical problem.
I'm not saying that you are, but my grandpa had the hiccups for almost two weeks straight before he passed on, and they were violent hiccups, you could hear him upstairs and he was in the kitchen, he couldn't sleep so I think that really contributed to his passing, I never heard what that was all about, I can't stand having hiccups for two minutes let alone two weeks, I would wish I was dead