if you have a fever & start getting a caffeine deprivation headache, try taking excedrin. it should help reduce the fever & get rid of your headache, AND, while it doesn't have much caffeine, but it does have some. According to the official excedrin homepage
each tablet has 65mg... so if you take two, you should be safe from those deprivation headaches (which are just evil even if you're not sick) .
of course, it's best if you just don't get sick to begin with. go eat some green veggies & take your vitamin C! (;