The `Teenage Dream` hitmaker - who is currently performing across the US as part of her `California Dreams` tour - has been forced to cancel a number of her concerts after suffering from "severe dehydration" as a result of the sudden illness.
According to a statement from promoters Jam Productions, the singer has rescheduled her July 8 show at Chicago`s Allstate Arena for August 21, and her July 9 gig at St. Paul`s Xcel Energy Center for August 23.
Katy said: "I apologise to my fans in Chicago and the Twin Cities for not being able to perform this weekend, but I am going to return in a few weeks to give them the very best show ever!"
This isn`t the first mishap Katy has suffered while on tour, as the star recently had to hire a cat whisperer to control her and husband Russell Brand`s trio of unruly felines, Krusty, Kitty Purry and Morrissey, who kept misbehaving while she was on the road.
She explained: "He realigned their chakras and did some hypnosis. We were like, `Wow, this is extravagant!`"