The Briton came second in the recent edition of the single-handed Vendee Globe around-the-world race, finishing in 74 days 19 minutes 35 seconds.
Despite damaging one of his two hydrofoils early on and suffering autopilot failure in a tense battle for the line, Thomson finished just 16 hours behind the record time of Frenchman Armel Le Cleac'h after almost 30,000 miles of racing through the world's most savage seas.
"It's the most physical and mental torture you can almost have," Thomson, 42, told CNN.
"Most people think we're crazy to do what we do but you have to be the opposite actually.
"The sport is about discipline, it's about eating and sleeping, keeping your energy up and managing your emotional levels.
"If you are not able to manage yourself, the best case is you make a mistake that means you're uncompetitive, the worst is you lose your life."
Thomson called it a "frustrating" race after he lost the lead when a submerged object broke a foil on his 60ft $5 million Hugo Boss yacht 13 days after setting out from Les Sables d'Olonne on France's west coast.
Offshore sailing is huge in this part of the world and a crowd of half-a-million people waved off the fleet of 29 solo sailors.
"There's not a dry eye in the house," says Thomson.
The setback fired him up, and he recalibrated his goals.
At one stage he set a new 24-hour distance record for single-handed monohulls of 536.8 nautical miles at an average speed of 22.4 knots.
Alongside the requisite sailing, electrical, hydraulic and engineering skills, plus heaps of courage and determination -- Thomson armed himself with a couple of secret weapons.
One was a wristband that gave him an electric shock if he overslept.
To keep the boat racing at optimum pace, Thomson would grab 20-40 minutes of sleep every two to four hours. His alarm was wired to a klaxon to wake him up. But if he didn't get up immediately, five minutes later he would receive a shock.
"I never once overslept because I never wanted an electric shock," he said. "It's safe but it's not very pleasant at all."
His other trump card was a custom-built bucket -- for calls of nature.
On modern stripped-out racing yachts like Thomson's Hugo Boss, facilities are of the "bucket and chuck it" variety, with a bio-degradable bag as a disposable liner.
To tackle the problem of buckets falling over when the boat is bucking like a bronco, Thomson's team developed a receptacle that can stay upright until 55 degrees of heel. That's handy for when the wind picks up just as you've settled down.
"It's made of carbon fiber and is probably the world's most expensive bucket. The seat is virtually molded to my bottom," said Welshman Thomson, the son of a search-and-rescue helicopter pilot.
Occasionally, fancy bucket or not, you literally can't go.
"Sometimes it's impossible," he says. "If you go down a wave and stop, the deceleration is enormous and you will be thrown from it.
"Obviously it's not very nice being thrown off the toilet, number one.
"But being thrown around the boat, there are lots of hard surfaces. It is really dangerous. Sometimes I wear a rugby scrum cap."
A less high-tech trick was what he calls his "turbo" boost to liven up the freeze dried food -- a bottle of Worcestershire sauce.
He describes the various flavors of cook-in-the-bag meals as looking like "slop," but says they give him the 3,500 to 5,500 calories he needs a day during the race.
Another treat was a packet of Spanish ham, until a friend pointed out it looked "sweaty and disgusting" in the tropics. The only alcohol on board was a miniature bottle of Champagne for Christmas, but in the end he didn't fancy it.
"It can be a bit of a battle to get enough food into you," says Thomson, who tucked into a cheeseburger as his first meal on shore.
"In the previous race I lost eight kilos, but this race I did well and didn't lose anything."
The attrition rate in the Vendee Globe is sky high -- fewer than 100 people have raced solo nonstop around the world successfully compared with more than 500 who have been to space.
Thomson's first two attempts in 2004 and 2008 ended early with equipment failure, before he scored a third place in 2012.
He's suffered some big scares, too. During the Velux 5 Oceans race in 2006 his yacht lost its keel nearly 1,000 miles south of South Africa in the Southern Ocean.
He owes his life to competitor and countryman Mike Golding, who turned back into a raging storm to rescue him from his life raft.
His yacht was also dismasted after being rolled by a rogue wave off the north coast of Spain in a transatlantic race in 2015. Thomson and partner Guillermo Altadill were airlifted to safety.
Managing the stress is "probably the hardest thing to do."
"It's relentless, from start to finish. Sometimes you think 'why?'" says Thomson, who likens experience of roaring along on autopilot to being a passenger in a high-speed rally car with no lights, at night, no windscreen and in the pouring rain.
"The hardest part is when you're in the south, and you're inside the yacht, it's dark in there, and the thing is moving all over the place.
"You're a thousand miles from help and if something goes wrong that's going to be it. Your brain is screaming at you that you're not comfortable, but somehow you have to be able to control the emotion, be able to reduce the adrenaline that's pumping through your body, get your heart rate down and be able to go to sleep."
Thomson has worked with sports psychologists to develop coping mechanisms. One is to visualize himself in a helicopter looking down on his yacht.
"You can see it going fast, you can see the waves are quite big, but not ridiculous, you can see there are no icebergs or container ships, and by doing that it allows me to calm everything down a bit," he says, though warns against completely desensitizing yourself.
Even on the difficult days, Thomson says he never feels lonely. He speaks to his wife and two small children regularly.
"Why would I be lonely? You can work in a big open-plan office with loads of people around and be lonely," he insists.
"I'm on my own but I know there are people who love me, I've got pictures of my family all over the boat, and I've got fantastic support. I could never feel alone.
"Is three months a long time?"
Despite the obvious dangers and privations, Thomson says he is "privileged" to be an around-the-world sailor.
"When you're on a sailing yacht or cruise ship and go out of sight of land you realize how small we are as a human race. It's a very humbling experience."
Amazing sunrises, sunsets and wildlife encounters are other unique perks.
"You become a bit blase about the wildlife," he told CNN World Sport. "You see dolphins virtually every day. The thing I love is albatrosses. They follow us in the Southern Ocean for weeks sometimes.
"They're so graceful and effortless, gliding just above the tops of waves. It's an amazing sight."
He found the homecoming to Les Sables d'Olonne "daunting." He didn't want a big fuss. Instead, more than 50,000 people lined the canal to welcome him back.
"I never think about the finish until the finish. Anything can happen. Then the whole emotion comes out," says Thomson, who took a couple of weeks to adjust to normal sleep patterns..
He's been third, he's been second. Thomson's next goal is obvious.