Think my cat is reacting badly to flea treatment?

i just put flea treatment on all three of my cats tonight cos i noticed a flea on one of them. i used revolution which is a liquid that goes on the back of the neck and i have used it on them quite a few times before with no bad reactions. but just now, one of them (male/desexed/4years old) started coughing. i... show more i just put flea treatment on all three of my cats tonight cos i noticed a flea on one of them. i used revolution which is a liquid that goes on the back of the neck and i have used it on them quite a few times before with no bad reactions. but just now, one of them (male/desexed/4years old) started coughing. i think he was grooming himself then he started coughing like he was gonna cough up a furball which he never does. is this something to do with the flea treatment? should i be concerned? i need to go to bed but worried i should keep an eye on him.
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