I've noticed that I get a head fogginess and sleepy feeling after I drink coffee. Weird, as it's caffeine...

I drink about 4 cups a day (at the most), slow drinking/sipping on it. I drink one full cup in the morning though, the rest is sipping, but why is it causing this head stuff?

Anyone else experience this with coffee? I drink it b/c it's warm and tastes good, not necessarily to wake me up or anything, I've never noticed a caffeine affect from coffee.

Just curious..