At her peak weight of 308 pounds, Jen Larsen would dream about getting skinny.
"I fantasized about it," Larsen, overweight since childhood, told ABC News. "It's the fairytale of weight loss. You lose the weight, and you are beautiful and you are happy."
Larsen's dreams drove her to undergo bariatric weight-loss surgery in 2006.
"I saw the before and after photos, and I leapt into it," she said. "I had tunnel vision. All I could see was this idea of me being thin."
Larsen, 39, of Ogden, Utah, did become thin - she lost 180 pounds. But she also found that as her weight went down, her unhappiness crept up.
"Being thin didn't make me happy," she said. "I'm still looking in the mirror, and I'm still hating what I see."
The unhappiness confronted by Larsen, which she wrote about in her book, " Stranger Here: How My Weight-Loss Surgery Transformed My Body and Messed With My Head," is not uncommon, experts said.
"Obese people live with the illusion, or the fairytale that if they lost the weight their lives would be better," said Dr. Bethany Marshall, a California psychoanalyst.
"What happens is, when they lose the buffer, they feel that people are scrutinizing them," she said.
Larsen said that after her own weight loss she too had to deal with what she called her "real psychological struggles," including depression.
Still, Larsen said she did not regret going under the knife to lose weight, and said her life was easier as a thinner person.
She did say, however, that it was important to look beyond just the number on the scale.
"I want my goal to not be a size and a number," Larsen said. "I want my goal to be strong and to run a marathon and to be comfortable in my own skin."
"I am pretty happy," she said.