The post widthdrawl Caffeine headache is caused by the internal "red alert" alarm your brain emits while it works to upsample, thus increasing the number of adenosine receptors on neurons to hear the messages that they should be hearing but aren't. Over the Caffeine high and trip, your body downsamples registering an over-supply and receptors, and it feels amazing it means you've got more than enough. Downsample = pleasure, upsample = pain.
Youtube Video: "This is your brain on caffeine" by This is your brain on science.
https://www.youtube.com/watch?v=YCIruyfw1OAThe plants that sprout 1,3,7 Trimethylxanthine in their beans or seeds from Colombia, South America, go through the effort to create these complex molecules our body mistakes for adenosine, because of the war of evolution and natural selection in plants vs herbivore mammals (our genetic ancestors). 1,3,7 Trimethylxanthine in the plant performs 3 jobs, it operates as an insecticide, herbicide and an addictive ingredient for animals that consume and distribute plant seeds through the digestive tracts. Caffeine is "plant sperm" waging addictive chemical warfare against herbivores. Caffeine effectively kills insects and the chemical is left to accumulate on the surface of the ground making the soil toxic for competing plants.
Youtube Video: Caffeine and Adenosine Receptors by Medicurio
https://www.youtube.com/watch?v=jOfquPE1cnU 
