The last thing The Biggest Loser's Sam Poueu remembers about the night of September 3, 2011 was a dinner party. "I had flown to San Francisco for a friend's birthday," he tells the new issue of Us Weekly. "We had sushi and sake."

Shortly after that meal, he suffered a devastating 54-foot fall and woke up in a hospital with a tube down his throat, suffering from a punctured lung, a severed kidney, a shattered pelvis, multiple facial fractures, a fractured tibia and a traumatic brain injury.

From what Poueu's fiancee, fellow Biggest Loser contestant Stephanie Anderson, can piece together, he went onto a friend's roof deck after dinner and upon realizing he was locked out, attempted to climb down the fire escape before falling four stories.

"When he hit the ground, his brain shifted," she tells Us in an exclusive interview. "He hemorrhaged and had a stroke."

Says Poueu, who spent three months in bed before learning to walk again: "Sometimes I try to remember the accident. But every time I go there, it gets dark and kind of eerie. I'd rather let it be and live."

For more on how Poueu leaned on Anderson during his hospital stay -- and how his desire to dance at their spring wedding serves as incentive to recover -- watch the emotional video above!