I was under the impression that drinking water upside-down worked for curing hiccups (when they worked) merely due to a placebo effect, or at the very least didn't work any better than just drinking water normally. In spite of this, many of my friends swear by it, saying it's the only 'cure' that works for them.
Is there any validity to this method of 'curing' the hiccups? I am most curious about minor spells which affect most people, not intractable hiccups.
Some background resources:
Hiccups are intermittent, abrupt, involuntary contractions of the diaphragm resulting in sudden inspiration abruptly opposed by closure of the glottis. The diaphragmatic contraction is often unilateral, occurring more often on the left side. Most hiccups occur as brief, self-limited episodes lasting only for a few seconds or minutes but sometimes may last for prolonged periods (> 48 hours), interfering with rest, sleep, and eating and causing fatigue, exhaustion, depression, and on occasion, death. In addition to treating underlying disorders, there are numerous methods to quell hiccups. Nevertheless, hiccups may be persistent despite a variety of therapeutic modalities.
Hiccups are an involuntarily powerful spasm of the diaphragm, followed by a sudden inspiration with a closure of the glottis. Hiccups that are caused by gastric distention, spicy foods and neural dysfunction can resolve themselves without any treatment. Some hiccups are associated with certain diseases or they occur postsurgically, and life-restricting intractable hiccups should be treated. The cause of hiccups should be quickly determined so as to administer the proper treatment.
Some anecdotal evidence:
"I cure my hiccups by filling a glass of water, bending over forward, and drinking the water upside down," says Richard McCallum, M.D., professor of medicine and chief of the Gastroenterology Division at the University of Virginia Health Sciences Center. "That always works and I firmly recommend it for my normally healthy patients."
That cure came through for musician Mark Golin, who found himself beset with hiccups after a late-night gig in New York City. "A woman told me to bend over and drink the water from the opposite side of the glass," he says. "It worked then and has worked dozens of times since then." 
 Feng-Cheng Liu, Acupuncture Therapy Rapidly Terminates Intractable Hiccups, South Med J. 2005;98(3):385-387.
 Ju Hwan Lee, Treatment of Intractable Hiccups. Korean J Pain. 2010 March; 23(1): 42–45