Jewish fasting
I fast for 25 hours (no food, no water, no nothin') during Yom Kipper, the day of atonement. The whole point is not to suffer but to alter your consciousness. You spend hours in the synagogue, praying, chanting and confession to sins that some Jew, somewhere might have committed (as a tribal people, if one Jew did it, all Jews are to some extent, guilty.)
We also contemplate our own mortality. One prayer asks "Who shall live and who shall die, who by fire and who by water?" and then lists other ways we might die and how God is with us anyway. These prayers are said aloud over and over throughout the two days.
At the end of the second evening, you feel vulnerable, yet elated. It's a combination of things at work here that causes this. Of course, at the end, we have a party or, as my friends and I do, go out to a Chinese restaurant.
I have a Christian friend who fasts (liquid only) for 40 days, at least once a year. He does it to offer up his suffering to God to get something he wants. It's never selfish; health for a sick friend, etc. I think it's nuts. I don't think God wants people to suffer. Also, it's wrecked his health, although he won't admit it.