Kelly Osbourne was filming her television show Fashion Police in front of a full studio audience when she turned to Melissa Rivers - daughter of comedian Joan - and said "I don't feel good", according to celebrity website TMZ.
The daughter of Sharon and Ozzy then reportedly fell out of her chair before the seizure begun.
An audience member, believed to be an emergency responder, ran up to help Ms Osbourne.
More top news
An ITV News investigation has learned that 99 children were treated on adult mental health wards in the first four months of this year.
Aside from the heat, lightning storms may have kept you awake last night; the Met Office have warned more can be expected tonight.
The temperature is a little cooler, but it's still a very warm day