The 54-year-old sports memorabilia dealer says he has had heart problems before. He had a massive heart attack less than a year ago just after the Palace Station incident.
Paramedics examined Fromong at the courthouse, but did not take him to a hospital because he refused treatment. His attorney, Louis Schneider, says Fromong was done for the day but could resume testifying on Tuesday.
Hours earlier they stopped the trial once before when Fromong, who says he use to call Simpson a good friend, broke down in tears.
O.J. Simpson made his way into the Clark County Courthouse Monday morning. He faces felony charges including armed robbery, kidnapping and conspiracy. He could face life in prison with the possibility of parole if convicted of kidnapping, and mandatory prison time if convicted of armed robbery.
Prosecutor Chris Owens says that Simpson was the ringleader of a "so-called" sting operation last year inside a Las Vegas hotel room. Owens says Simpson's goal that night was to steal high dollar sports memorabilia.
"We are going to spend the next few days finding which may be the true face of James Orenthal Simpson," said Chief Deputy District Attorney Chris Owens.
Defense attorney Yale Galanter told the jury that the sports memorabilia was in fact stolen from Simpson several years ago and he was just there that night trying to get it back.
"I submit to you that at the end of this case you will determine that Mr. Simpson is not guilty of committing any crimes, because he never has the intent to commit any crimes. This was a recovery, not a robbery," said Galanter.
Fromong was the first witness called to the stand. He recalled that night at the Palace Station when O.J. Simpson along with four others stormed into the hotel room.
"He was shouting, 'How could you steal my stuff. I thought you were a good guy. You sold my stuff.' There was a lot of shouting and he said, 'Don't let nobody outta here ... stand the (expletive). Nobody gets out of here,'" said Fromong.
Jury selection took four days before Judge Jackie Glass had 12 jurors and six alternates sworn in late Thursday. Trial is expected to take about six weeks.