It is thought that the longest bout of hiccups was suffered by an American called Charles Osborne who started hiccuping in 1922 and carried on for another 60 years, although he did live a relatively normal life and died aged 88. But is must also have been hard on his nearest and dearest and it is unclear what happened when he slept, since it must have disturbed his sleep significantly.
Hiccups are caused by involuntary spasms of the diaphragm which is the muscle that separates the chest from the abdomen.
Simultaneously as the diaphragm spasms occur, the larynx (the upper windpipe) actually closes involuntarily.
What causes the irritation of the diaphragm (and therefore causes the hiccups) can vary from person to person. Some people get hiccups after eating too quickly, an overfull stomach or too much alcohol. It may also occur when there is an inflammation of the membrane around the heart.