When you drink coffee everyday and then suddenly stop, I was told your blood vessels close up in your neck and that caused a headache.
Caffeine is a vasodilator, which in laymans terms means it opens up the blood vessels. Caffeine is sometimes used to relieve headaches caused by the restriction of the blood vessels in the brain. Presumably then, the opposite might occur to an avid coffee drinker who suddenly stops drinking.
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The answer is completely wrong :(That's exactly the problem of internet - smth.looks like a serious staement, while actually is a desinformation. In case of health issues it may lead to unpredictable consequences...