The BBC show filmed in Colchester town hall, Essex, was suspended while a woman was given first aid.
Question Time host David Dimbleby said they had to stop filming because the woman “could not be safely moved”.
Simon Crow, 52, from Colchester, told Express.co.uk: “The question was about new homes being built, which is a hot topic in Colchester because of overdevelopment.
“I was in the second row and the lady was in the front row at the end, about six feet from me.
“I could see her out of the corner of my eye and she fell on the floor sideways. The floor manager told everyone there was a situation.
“People got up and started attending to her. A local councillor, who was Mayor of Colchester last year, dialled 999.
“David Dimbleby went over himself to see what was going on.
“After about 10 minutes, maybe 15, paramedics came and started attending to the woman.
“We didn’t know if the show was still going on, but then Dimbleby said they had to call an end to the show.
“The floor staff got everyone out, but they said the woman could not be moved for an hour. We left and they attended to her.”
The programme be will broadcast in a shortened form.
In a statement on Twitter, BBC Question Time said: “Further to our earlier statement, an audience member on tonight’s QT was taken ill.
“Our first priority was to make sure that she was looked after by medical staff who attended. As a consequence tonight’s Question Time was slightly shorter than billed.”
The panel had been asked “what is the point of capitalism?” and whether the budget could fix the broken housing market.
The hour-long political programme features Labour Shadow Home Secretary Diane Abbot, Conservative MP for Tunbridge Wells Greg Clark, former Metropolitan Police commissioner Lord Hogan-Howe, former CEO of Marks and Spencer Lord Rose and crime writer Dreda Say Mitchell.
More to follow…