Feeling miserable for three days seems ... unlikely after 800mg/day of caffeine. I say that to mean, it should be much longer (been there, done that, took many months) Caffeine use especially at that level massively grows the amount adenosine receptors your brain has, and they don't just disappear overnight.
A 500ml Diet Coke (assuming you don't mean the caffeine free version) also contains about 65 mg of caffeine, which is the same as an espresso. I'm not sure if you really quit. Caffeine is also in a surprisingly large amount of soft drinks you wouldn't expect.
A 500ml Diet Coke (assuming you don't mean the caffeine free version) also contains about 65 mg of caffeine, which is the same as an espresso. I'm not sure if you really quit. Caffeine is also in a surprisingly large amount of soft drinks you wouldn't expect.