^!!! I had a cat that developed an allergy to topical pest medicine and had the SAME response. The vet told me to wash it off of him with Dawn dish detergent...it'll cut the oil better than regular pet shampoo...and then never use it again. I switched to a flea collar for him, and then he was okay. The vet said it was a serious reaction and could have worsened if it wasn't washed off...could have caused intestinal bleeding, I remember.
Good luck to your kitty.