With only several days left before his 6-month contract expires, Southall wrote in his Web blog that he was stung by venomous jellyfish Irukandji, which is the size roughly of a fingernail.
"I've avoided being boxed by a kangaroo, nibbled by a shark and bitten by a spider or a snake - but then in my final few days on Hamilton Island I fell foul of a miniscule little creature known as an Irukandji," Southall wrote.
Irukandji, which are mostly found near Australia, contain venom that can be lethal to humans, but local doctors treated Southall in time and after a good sleep he recovered.
"I was feeling pretty hot and sweaty, had a headache and felt pretty sick too, together with pain in my lower back and a tightness in the chest and a really high blood pressure - all classic symptoms of Irukandji syndrome," he said.
"The doctor knew instantly what it was and straight away started the course of treatment to get me on the mend, I had a couple of injections which immediately took away the uncomfortable pain I was feeling and I slipped into a comfortable sleep after an hour or so," he added.
Southall was chosen out of more than 34,000 applicants from around 200 countries in May.
According to the contract, he is paid $150,000 for six months to live in the Blue Pearl villa on Hamilton Island overlooking the Coral Sea, with a swimming pool and a golf course.
His job consists of publishing a weekly blog and video and photo diaries, as well as feeding fish and turtles and collecting mail.
Benefits of the "dream job" also include free flights home with all food and accommodation included in the package.
The Best Job campaign was launched by Australian tourism authorities in January in an effort to attract tourists to the country amid the global financial crisis.