They included three civilians and two paramedics.
Members of the NI Ambulance Service were attending an incident at a house in Newcastle on Friday night when they started to feel unwell.
Four ambulances were sent to the incident.
The crews were helped by teams from the Fire and Rescue Service in treating themselves and three others with oxygen.
The five people have been taken to the Ulster Hospital in Dundonald in east Belfast where their blood levels are being monitore.