It is a queer fact, well known among even casual readers of magical history, that hiccups are a sign of the afflicted having recently stood near the Bleak Place, the threshold between the human world and the Otherworld.
This is why children are more susceptible to hiccups that adults. Children, with their innate, uncorrupted knowledge of magical things, are more likely to believe in the truth of the Otherworld, and are thus more prone to infringe upon its boundaries.
A small number of children, the disappeared, have accidentally crossed the threshold. These are always the children of un-schooled, simple folk. So their parents, having no understanding of magical history and the ways of faeries, despair for their children. They despair because they do not know that human children are upheld as Royalty in the Otherworld. To faeries, children are Princes and Princesses. One child, much beloved by the faeries, was made their honorary King and was seated on his own specially constructed throne on the days of faery festivals.
Human children can only enter the Otherworld accidentally. No human being who has deliberately attempted to make the crossing has ever been successful. Faeries, on the other hand, can cross into the human world at will. Their path into the human world can either be direct - though this is difficult - or via a human host. When a human comes close to the Bleak Place, a waiting faery can fly across the threshold and into the human's mouth. If the faery manages to stay inside their host's mouth until the human leaves the threshold, then it has entered the human world.
The problem, of course, is that a human with a faery in his or her mouth will be afflicted with hiccups. The faery can only escape during a hiccup, or if their host receives a fright.
Ignorant human beings, not knowing the cause of hiccups, believe a drink of water to be the cure. This is a grave danger for faeries entering the human world. Water cures hiccups by choking the faery to death. Strong faeries can survive a good soaking, but many drown in this way.
The proper cure for hiccups is patience. The faery will escape eventually.