The 28-year-old, who reached the pinnacle of his career when England became world champions in 2003, admits he came close to quitting the sport following an alarming slump in form after lifting the William Webb Ellis Trophy.
The Northampton captain has not played for his country since last year's RBS 6 Nations but is back in the fold under new head coach Brian Ashton for this year's tournament.
It is a remarkable turnaround for a player who considered hanging up his boots less than five months ago.
"It wasn't dramatic and it wasn't sudden - but as each week passed, I played worse," he said.
"My energy levels dropped and so, too, did my enthusiasm for the game. It got to the state where I was so fed-up I thought of quitting."
Instead of throwing in the towel, Thompson resorted to drastic measures to rediscover his motivation which has slowly but surely returned this season.
"Before (former head coach) Andy Robinson was able to tell me he was resting me for last summer's tour to Australia, I had made up my mind to pull out," he said.
"I'd fallen out of love with the game. I went to Thailand and endured a 10-day 'detox' that saw me lose seven kilos and go through colonic irrigation each day.
"Even when I came back to pre-season training my heart wasn't fully in it. But from around October I started to rediscover my old form.
"A four-week calf injury prevented any chance of a recall for the autumn internationals, but I've been playing well since and I'm delighted to be back in the fold.
"I'm on 47 caps and I want to reach my half-century, help England have a successful Six Nations and go on with confidence to the World Cup.
"I think not being part of England has helped me and others such as Mike Tindall and Jason Robinson, who have also been recalled.
"We've all realised how much we've missed playing for England, and the hunger's returned.
"I'm also excited that Phil Vickery is captain and I'm convinced he will prove an inspirational leader."