the next time i need to go to sleep, i just have to drink some coffee. its confirmed. every time i drink coffee, i feel drowsy and extremely sleepy! well, 90% of the time. the remaining 10% of the time, it perks me up for an hour, then comes in the sleepy feeling. usually, this 10% applies if its my first time to drink a certain type of coffee. so i guess, by the 2nd time i try the coffee, my body has created an immunity from its stimulating effect.