because you are way too tired?????
I think people react differently to caffeine.... I never lose sleep over having caffeine and my wife can't sleep at night if she has cup of coffee after 3 pm....
Does this happen all the time when you drink coffee?
Do you load your coffee with lots of sugar and milk? I'm wondering if you get a short burst from the sugar, and then experience the let down when your sugar level drops....could that be what's making your feel sluggish or sleepy?
Sugar will boost up your energy and when it comes down it can make your sleepy.... It might not be true for everyone but some people have more effect....
Speaking of coffee chemistry......I used to spend a lot of time exploring the Internet, gathering coffee-related information, and I recently remembered that I stumbled upon a Coffee Chemistry website.
I just found it again. It has a lot of interesting information, including lab equipment and technical kits that I never knew existed. It may be worth a look.
Sugar is bad for you, go organic coffee, tea and go off dairy you will feel great straight away. Organic Soy is an alternative. I buy my coffee from Global Organic Coffee, it tastes and makes you feel amazing like a vitamin.