The American Airlines flight was diverted after two flight attendants reported dizziness and four passengers fainted.
An airline spokesman says the pilot dropped oxygen masks after being notified by flight attendants about the dizziness.
The spokesman also says all 132 people on Flight 547 from Reagan National to Chicago's O'Hare Airport, walked off the Boeing 737 after it was diverted to Dayton. He says two passengers and a flight attendant were taken to hospitals.
The passengers were able to return to the airport and accompanied their fellow passengers on a replacement plane to Chicago. The flight attendant was admitted for overnight observation.