I ran out of
coffee last week - had the last cup before bed in the evening as you do (well..as I do anyway

)
The next morning I had tea and thought nothing of it. Later in the day a head-ache started up. I had panadol but to no avail. Felt absolutely horrible.. and then it hit me that i was in cafeine withdrawal.
Yep...I'm addicted. Having one to go to sleep must be an advanced sign