:S I hope your kitty gets better really soon.
And yes you have to be careful with flea and tick medications, recently I heard of a case of 2 cats, same medication (it wasn't Assurity) one had no effects at all the other cat had a bad reaction to it, started getting weak, vomiting and diarrhea after like 1 hour of administrating it. The owners took him to the vet immediately now he's fine but it was a dangerous episode.
Also a vet told me a really tragic story about people that without knowing used tick medication for dogs on a cat. Immediate reaction, the poor baby died in about 30 mins from poisoning
He told me "NEVER ever use dog medication for ticks on a cat". I never forgot that warning.
Thanks for the heads up.
Mine are indoors so they don't get fleas but you never know, and it's good to be aware.