Llhrei'sian (pronounced racy-on) was a sickness that affected Vulcans and Romulans, as well as other races on occasion. (RIS Bouteina)
Pazzo claimed that his daughter could win the Ignobel Prize of Medicine if she somehow published a paper concerning the effects of Duff beer on llhrei'sian. (RIS Bouteina: "Doctor Rihanna")
Subspatial llhrei'sian
Humans and Byzatium could not have subspatial llhrei'sian through subspace turbulence, unlike Romulans, where a Grust 5 turbulence and higher could cause the malady. Its name, literally translated to English, meant diarrhea. In a sense, the people afflicted from llhrei'sian suffered from diarrhea, but the sickness also dulled one's senses and balance.
There were other causes to the malady but the cure for that form of llhrei'sian, cyprofloxacine, was not replicable. The shortage of the remedy aboard the Bouteina almost made the crew mutiny and mandated an away mission to get some more. ("What about some D'oh!")
Also, coffee could help alleviate this kind of llhrei'sian by accelerating the purging of one's excrements, just like any laxatives can. ("There's no Coffee in the Nebula")
Food poisoning
Vox'ula, after eating Krusty burgers, has suffered from that form of llhrei'sian while on an away mission on Simpson's Planet. Duff beer proved to be a cure for his food-induced llhrei'sian. Non-Romulan speakers usually refer to this form of llhrei'sian when they speak about llhrei'sian. (RIS Bouteina: "Fundraiser")
External link
Traveler's diarrhea article at Wikipedia, the free encyclopedia.