"They are guessing a little bit of a combination of fatigue, his schedule recently and diet and sleep and all those things that kind of came together during a hectic day," Reifert said. "He felt a little faint. They automatically treat it as severe.
"By the time he got to the hospital, he was coming out of the ambulance joking. He was being Jerry. He was joking and talking. You knew then that he was fine. It was just a matter of then running tests to make sure it wasn't something cardiac-related. It wasn't."
This medical episode happened to Reinsdorf during a dinner he was attending with Hall of Fame inductee Frank Thomas. In his pre-induction session with the media Saturday at The Clark Sports Center, Thomas expressed the feelings of immediate concern and immediate fear for his friend and former boss on Friday night.
"He was doing great, and all of a sudden feeling faint and he fainted," Thomas said. "We all just started thinking of all the scenarios. He was down for a while. That scared the [heck] out of me. He was down for a long time, and it didn't look good. ... To see them take him away in an ambulance, we thought it was serious.
"You can't take life for granted. We are going to enjoy the rest of this weekend. But that was really, really stressful. I'm so glad he's doing well."
Aside from not getting a good night's sleep in the hospital, Reinsdorf was ready to resume the Hall of Fame weekend's activities per Reifert.
"He came back to the hotel, slept a little bit, had lunch and was relaxing," Reifert said. "He's hoping tonight to be part of some of the festivities. And hopefully he's 100 percent Sunday and we'll go just like he planned."
Scott Merkin is a reporter for MLB.com. Read his blog, Merk's Works, and follow him on Twitter @scottmerkin. This story was not subject to the approval of Major League Baseball or its clubs.