Some good advice from Rappie there. Also watch for coughing or gagging (like a cat with furballs), vomitting, refusal of food, or halucinations (dog barking at something only it can see).
The reason for the medication is, even if you groom your Cocker daily, a tick that's on the dog for only 20 hours or so can still do a lot of harm before it's discovered... the poison still circulates in the dog's system even after the tick's removal, so preventing the bite in the first place is vital. Tick prevention medication alone won't act against the effects of the poison once it's in the dog's system, an anti-serum will be required after that point.
Don't be frightened about this aspect of Cocker ownership... Most Cockers love to be groomed and a well cared-for coat will keep your dog looking it's best and make checking for ticks a breeze.