I remember (or, more accurately, half-remember from a long-ago and half-forgotten source) hearing that hiccups are like a “mistake” in the way your body processes oxygen (on the chemical level, of course - it’s hard to make a mistake in the mechanics of breathing).
Thus, I have found a solution that works, at least for me, every time.
It’s holding your breath. The trick, however, is to hold your breath until you’re nearly ready to pass out; until real panic begins to set in. This (I think) depletes enough of the oxygen from the chemical pathways that it will “reset” your oxygen pathways and break you out of the self-reinforcing cycle of hiccups.
Unfortunately, depriving yourself of oxygen like this probably kills brain cells. But isn’t the loss of consciousness supposed to protect your brain from a lack of oxygen? And you’re not depriving yourself of oxygen enough to trigger a loss of consciousness, anyway, right?
I find it is more than just holding your breath. I have to bear down on the diaphragm, like I am trying to go to the bathroom sorta. That pressure on the diaphragm seems to do the trick for me, I almost never get more than three hiccups in a row.
In the past week I have gotten a case of the hiccups three times, and each and every time, my remedy has been to drink water upside down. For example, take cup of water in hand, bend forward and place your mouth on the far side of the rim, and lean farther forward until you are able to drink from the cup. Take a few swallows and voila, hiccups are a thing of the past. At least for me.