Caffeine doesn't have a strong psychological addiction, but it's physiological withdrawal symptoms are bad.
All these fake coffees (I’m looking at you, chicory root) taste like ash-trays from the grimiest bar in town.
I didn't have a coffee maker at home at that time. So I started getting headaches on Sunday. I made the connection eventually, after my headache completely disappeared 20 minutes after drinking a cup of coffee with a friend.
This appears to be a pretty common scenario.