Coffee,Sugar, and sleep...?!

Best Answer - Chosen by Voters

When you have sugar, your body produces a dose of insulin to get rid it (convert it to something storable by the body). Unfortunately the body usually produces more insulin than is necessary initially, so your blood sugar level ends up lower than before. This tends to happen if you are inactive. I believe if you are excercising this doesn't happen.

This is also why you can feel really tired after a meal with high glycemic load.

A-Level biology

are you eating a donut or a sugary pastry with your coffee? if so that's the problem. youre eating too much sugar, which causes your sugar level to drop, and that makes you sleepy (regardless of how much caffeine you drink). its the same effect you get when you eat a big bowl of pasta. if youre not eating a pastry, then you must be putting a heck of a lot of sugar in your coffee! 1 or 2 tablespoons shouldn't make you sleepy like that.