Aspen police Sgt. Bill Linn said the four-star general told him it appeared to be a combination of altitude sickness and something he ate.
"He is conscious and in very good spirits," Linn said shortly before Powell was released from Aspen Valley Hospital at 1:45 a.m. Linn said Powell asked him to speak with reporters.
Powell's secretary, Peggy Cifrino, said that Powell called her at 2:30am EDT to tell her that he was fine, CBS News' Charlie Wolfson reports.
A nursing supervisor at the hospital, where former Enron CEO Kenneth Lay was rushed to and pronounced dead early Wednesday, refused to comment.
Powell, 69, was in Colorado for the Aspen Ideas Festival, a conference in its second year that invites some of the world's leading thinkers.
Cifrino said that Powell was out and about this morning, attending some sessions of the Festival, Wolfson reports.
The former chairman of the Joint Chiefs of Staff and chief strategist of the 1991 Persian Gulf War against Iraq served as President Bush's secretary of state from 2001 until January 2005, when he was replaced by Condoleezza Rice.