What Causes Drowsiness After Drinking Caffeinated Coffee While On Prozac?

Whenever I drink caffeinated coffee I get very sleepy. I'm currently also taking prozac for depression. I maybe have one coffee a week. Today I had espresso around noon. Immediately after I had the coffee I got very sleepy, very similar to the feeling after having 4-5 alcoholic drinks, only without the euphoria. Tired, confused, dizzy, slowed down. Though I haven't had any more today, it seems to be getting worse. Now, 7 hours later, I am thinking about going to the hospital. What should I do?