When she stopped competing, Forrest, now 49, felt "sort of heartbroken", she told the Weekend Herald yesterday. "It was a relationship you had with the water - your first major relationship - and you've broken up with it."
Over the next decade, she worked in four different jobs in TV and radio, and also went to New York to study acting.
"I couldn't work out Lisa Forrest, so I thought, 'I'll play other people'. I was jumping around like a jack-in-a-box, trying to find myself. I was all over the place. Eventually I found my way, but it was very turbulent."
In some ways, she was better equipped than Thorpe. Competing before the Olympics effectively turned professional, Forrest never stopped being a schoolgirl. She wrote English essays in between fielding calls from journalists, and experienced from an early age "the incredible high of winning a medal, then having to come back to reality".
Thorpe, now 31, began training at the age of 9 and grew up in the public spotlight, surrounded by coaches and managers. After announcing his retirement in 2006, he made a failed comeback before the 2012 London Games. He then set his sights on this year's Commonwealth Games in Scotland, but a shoulder injury ruined his chances.
Although he has dabbled in fashion design and TV work, he seems not to have found an outlet for the energy and passion which he poured into swimming. He has continued to face questions about his sexuality, and reportedly has financial problems. Those troubles have been exacerbated by the depression which he revealed in his 2012 autobiography This Is Me, and which drove him to abuse alcohol at times - even as he was winning medals.
Nearly all elite athletes find the switch to mainstream life tricky, says Kirsten Peterson, head of performance psychology at the Australian Institute of Sport (AIS).
"If you look across any performance realm - movie stars, what Miley Cyrus is going through now - people are put into situations where the attention is so intense, and they reach success so early, they haven't developed the skills to deal with it. It's like winning the lottery then going broke, because you don't know how to spend the money."
Research by Paul Wylleman, a sports psychologist at the Vrije University in Brussels, stresses the importance of normalising retirement by discussing it with athletes almost as soon as they reach elite level. In practice, though, most athletes are loath to address it. "It's almost like a superstition - if I talk about it, it'll happen," says Peterson.
The AIS organised transition seminars after the London Games, "but it was like pulling teeth to get athletes to come ... We had to cancel some of our scheduled events," remembers Peterson.
Thorpe's latest, and well publicised, bout of depression has prompted public expressions of sympathy from a whole parade of former Olympic and marathon swimmers, who also recalled their own battles. Grant Hackett, Libby Trickett and Geoff Huegill suffered from depression. Michael Klim found the transition "pretty tough". Susie Maroney struggled with an eating disorder.
Yet Grant Brecht, a sports psychologist who works with the Sydney Swans AFL team and Sydney Roosters rugby league club, says the rate of clinical depression and anxiety disorders among elite athletes is no higher than in the general population.
"It's a microcosm of society, but one that gets a lot of media spotlight."
It was seven years before Forrest set foot in a swimming pool again. She was physically exhausted when she retired, and "hated" the water. "I didn't speak about it at all. I deliberately ran as far as I could away from it."
In New York, she saw the huge Matisse cut-out The Swimming Pool at the Museum of Modern Art. "It revealed to me everything that was exquisite and sensual and beautiful about being in the water," she says. "I went out that afternoon and bought some swimmers."
