You have to catch them early like that or you can end up doctoring for years. One co-worker has a kid that can't seem to kick Lyme disease, and those folks were careful in the first place, but they are so thick around his home that he picks up deer ticks mowing his lawn.
It pays to look for the bullseye even if you didn't notice the tick. You may not find all of them before they drop off. And just because the bullseye goes away doesn't mean that you no longer have the infection. Get it tested and treated as soon as possible.