The 27-year-old welder, who lives near South Bend, survived nearly a week in the cold in December.
He said he was driving home from work when he crashed along a creek beneath I-94 in Porter County.
"I see a pair of what looks like deer's eyes in the middle of the road, and I swerve onto the shoulder and I go to swerve back onto the highway, and by then, the guardrail had already popped up," Reum said.
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Two fishermen found Reum on Dec. 26, six days after that crash, pinned inside his mangled pickup truck.
He said the rain that fell during that time helped to keep him alive.
"I take kinda that visor that covers up the sunshade, and I can kind of put a bend into it where that'll just funnel all the water," Reum said. "And then, drink the water through the sweatpants, trying to filter out any kind of the debris or anything like that."
Doctors had to amputate part of Reum's leg, but he has kept a positive attitude through his entire ordeal.
He now plans to write a book, become a motivational speaker, and eventually return to his love of running.
SEE MORE: Matt Reum, Indiana crash victim stuck for days under I-94, thanks public for support from hospital