Reacting to flea treatment?

[HPparent]

Cat was prescribed Frontline flea treatment by the vet as a preventative measure. Cat was given a dose last night and has been hiding in the bathroom and drinking a lot ever since. DH just informed me that he noticed a sore patch of skin after the last treatment a month ago but decided to go ahead anyway grrr. I haven't examined her skin, but wonder if she is in pain?

Should I bring the cat to the vet or is there anything else I can do to help her.

I've heard about some cats getting a skin irritation from flea products. Why not phone the vet and ask what they suggest?

Cat came out of the bathroom and started eating soon after I posted, though not as affectionate as usual or doing her sunbathing, though she doesn't seem ill.

I cannot see any irritation at the site - she won't let me examine her closely, but last time it was on her head, so she may have been irritating her and she scratched there instead of the back of the neck.

I didn't call the vet, but will take her back next month and see if there are any alternative products. She tried to run and hide when she saw it last night.