Causes for hiccups??????

i get hiccups severly! usually lasts for anywhere between half an hour, and several hours. last night it was going on for almost 8 hours! and they actually cause pain after a while coz the amount of hiccups. ive tried holding my breath, drinking lots of water, getting scared, and was so despirate i drank water while upside down. are there any particular causes for hiccups and is there any other ways to stop it????