It's the middle of October in the Top End, the season also known as "the build-up". The harsh sun glares down from on high and the humidity is so thick you can almost see it — but there's not a cloud in the sky and no sign of relief.

And there won't be for months.

You're angry, irritable, and feel as though the tiniest thing might send you into a frenzy.

As any resident of the tropics will tell you, these are the symptoms of "going troppo".

This investigation is part of Curious Darwin, our series where you ask us the questions, vote for your favourite, and we investigate. You can submit your question or vote on our next topic here.

Melvyn Lintern, originally from England, wrote to us wanting to know if there was any truth to the condition.

"I came to Perth in 1980 and was warned about the danger of going troppo up north within a week of arrival," he said.

"For an impressionable young Pom, the dangers of Australia were known to me — snakes, crocodiles, sharks, redbacks, drop bears — but this sounded more sinister.

"Something that could affect your wellbeing, contagious, maybe incurable. How was it transmitted?"

What's the evidence?

Are you actually losing it during the constant, oppressive, humid heat, or does it just feel like it?

There is science behind the madness, reckons Dr Mary Morris, a senior psychology lecturer at Charles Darwin University.

"I think going troppo is a real thing," she said.

"Whether it's a collection of symptoms, whether it's a syndrome, how it manifests in different people depends on a whole lot of things. There's no question that people can feel it."

Research co-conducted by Dr Morris has linked tropical heat with a range of physical and mental ailments.

"They feel different moods, and they feel different levels of depression, anxiety, stress; things like that," Dr Morris said.

"You do behave differently, and you're more depressed, and you've got less energy, and you're sadder. Life is just really tough."

Tropical summers = northern winters?

Dr Morris doesn't believe going troppo is an actual disorder, but rather a collection of behaviours and emotions influenced by heat.

In fact, research has found these seasonal symptoms are similar to those shown in people experiencing northern winters with sunless days.

"If you look at… what happens with sleep deprivation, then you can see how some of that are the symptoms of going troppo," she said.

"It's the same symptoms for a different reason. Up north when you've got no sun and it's cold and it's miserable, people get depressed."

Heat hangovers? You bet

Thermal physiologist Dr Matt Brearley also believes there's a case to argue for going troppo.

"Not based on anecdotal evidence… but based upon the science," he said.

Heat stress consultant Matt Brearley and an ingestible pill that communicates core body temperature in real-time. ( ABC Radio Darwin: Jesse Thompson )

Dr Brearley works with tradies, teaching them how to keep cool while they're working in the Top End heat.

"We see a change in both the response of workers to heat at work, and their responses in the home environment during the October to April [wet] season," he said.

Dr Brearley said worker's sleep patterns, appetites, relationships, and hobbies were all affected by continual exposure to high humidity and temperatures.

To add insult to injury, heat-related stress has even been found to cause "heat hangovers".

"Day by day, being exposed to the heat has an effect on workers," he said.

"And we start to see these symptoms like an alcoholic hangover… but it's due to heat.

"So they have the nausea, headache, loss of appetite, and general lethargy."

'Going troppo' a hot topic

So it would seem the phenomenon of going troppo isn't just a Territory tall tale. But where did the term come from?

Troops stationed in the Pacific experienced the "troppo" phenomenon ( Australian War Memorial: Damien Parer )

The earliest evidence of use of the word "troppo" can be traced back to 1941, said Dr Amanda Laugesen, director of the Australian National Dictionary Centre (ANDC).

"[It was used] to refer to someone who's mentally disturbed… as a result of spending too much time in the tropics," she said.

According to Dr Laugesen, the word was widely used by Australian troops serving in the Pacific.

"With troops being stationed both in the north of Australia and in the Pacific, they were having that experience more often than not," she said.

"It was a handy term for them to be using."

Made for Darwin, in Darwin

The term first appeared in a Darwin publication called Army News, Dr Laugesen said, and became very popular, very quickly.

The term "troppo" first appeared in Army News in 1941, Dr Laugesen said. ( Supplied: National Library of Australia )

"There's quite a lot of discussion in 1942 if you look at contemporary newspapers… they sort of refer to the Darwin boys as having coined this term," she said.

"The first evidence is from 1941, and then in 1942 everyone is talking about it.

"So, from 1942 there's evidence for the phrase 'go troppo', 'gone troppo', 'going troppo', and continues right through to today."

Dr Laugesen said the lack of earlier evidence means it's quite possible the Australian Imperial Force soldiers in Darwin were behind the term.

"I think the idea is that they were bored, they were hot, they were tired of being there; they were going a bit troppo," she said.

Despite the term's earlier origins, it's now used in a much broader sense.

"Advertisements saying, 'go troppo, buy a holiday to Queensland', or 'add something to your menu, go troppo' and add something that reminds you of the tropics," she said.

"And also, the idea of just going a bit wild, a bit crazy, is definitely a connotation that's evolved in the years since World War II."

Our question asker, Melvyn Lintern, said he was particularly interested in the history of the phenomenon, and in light of the new evidence, now wondered if Indigenous people ever experienced it.

"Probably not, as they originated from even further north," he said.

"They probably felt a sense of relief when they moved further south, though!"