Petraeus had just finished answering a question when his head went down on the table while Sen. John McCain (R-Ariz.) was telling him he was an American hero, NBC News reported. McCain got a strange look on his face and the camera went back to Petraeus with his head on the desk.
Several people rushed to help and a recess was called.
Petraeus, walking without assistance, was then escorted quickly out of the room, according to the Associated Press. His spokesman could not be immediately reached.
Sen. Carl Levin (D-Mich.), the chairman of the Armed Services Committee, said Petraeus was "doing very well" and that he was eating and didn't have enough water to drink in the morning.
"He appears to be doing much better," Levin said.
Petraeus, commander of U.S. Central Command, was testifying on the war in Afghanistan. His testimony was rescheduled for Wednesday.