Just the change of diet could have done it CJK - some cats are just sicky cats unfortunately - my Jenny is one
As has been said on other threads, if the cat is alright in themselves - still affectionate, washing/taking care of themselves/normal personality and most importantly still drinking water, then it's good to wait a day or so before panicking.
Eating grass can make cats barf too - but the grass is good for them in some way, of course as long as it's "clean" - pesticide-free
Not for the faint-hearted:
I lost Lucy-fur in 1994 to suspected poisoning. The sick really did smell ***bad*** - it's indescribable (luckily) but trust me, I think you'll be able to tell from that if there's something more wrong than furballs or eating too fast, or just plain being a cat!
