Photo: Brian Cassey/AP

We still have a couple months before Shark Week mania sets in, so in the meantime, here’s a PSA that some of the worst things about the beach are often much littler than sharks: biting sandflies, grains of sand lodged in uncomfortable places, oddly shaped patches of burned skin from the spots the sunscreen missed. Also, tiny jellyfish whose stings make you acutely aware of your own mortality.

Look, I’m not much of a beach person to begin with. But I’m decidedly less so after reading about the Irukandji, a collection of jellyfish species less than an inch long whose sting causes symptoms so severe and so bizarre as to have a medical condition named after them. Irukandji syndrome is characterized by vomiting, headache, anxiety, cramping, and — most distinctively — a state that scientists have described as “a feeling of impending doom.”

“Patients believe they’re going to die and they’re so certain of it that they’ll actually beg their doctors to kill them just to get it over with,” Australian biologist Lisa Gershwin told ABC radio in 2007. They won’t die, as long as they get medical attention, but they will experience a cornucopia of other hellish sensations, as Gershwin explained:

It gives you incredible lower back pain that you would think of as similar to an electric drill drilling into your back. It gives you relentless nausea and vomiting. How does vomiting every minute to two minutes for up to 12 hours sound? Incredible. It gives waves of full body cramps, profuse sweating … the nurses have to wring out the bed sheets every 15 minutes. It gives you very great difficulty in breathing where you just feel like you can’t catch your breath. It gives you this weird muscular restlessness so you can’t stop moving but every time you move it hurts.

Irukandji syndrome received its name in the 1950s, after an indigenous tribe in Queensland, Australia, where members frequently displayed this puzzling collection of symptoms. The story of how it came to be connected to stings is horrifying in its own right: In the 1960s, an Australian scientist named Jack Barnes captured a couple of jellyfish and, to confirm his hypothesis, used it to sting himself, a lifeguard, and his 9-year-old son. (He also, it’s worth noting, played it off pretty casual in the subsequent paper, like he hadn’t just sentenced his own kid to a lifetime of trust issues: “The first Carybdeid was applied to an adult (J.B.), and to a boy, aged nine years (N.B.). A robust young life-saver (C.R.) volunteered to test the second specimen, of similar size to the first.” If Barnes got this paper past an IRB, it’s probably best that we don’t know how.)

Irukandji jellyfish are common in Australia, but people have suffered their stings around the world, including in Malaysia and the Caribbean. At the U.S. Army Special Forces Underwater Operations School in Florida, The New Yorker reported last year, more than a dozen cases of Irukandji syndrome have been documented.

In 2014, io9 described a few other things that can bring on the same sense of impending doom: cardiac arrest, understandably, is one of them; nutmeg overdose, less intuitively, is another. Researchers aren’t sure what causes the feeling in Irukandji sufferers, but research on animals suggests that the venom causes an uptick in the hormones adrenaline and noradrenaline, which are connected to anxiety. There’s no antidote —treatment is just managing the symptoms — but in the meantime, here’s some advice: If you do get stung by a jellyfish, don’t pee on the sting. That’s an urban legend. Also, wear lots of sunscreen. The beach is full of lurking danger; it’s best to play it safe where you can.