For me the reason is simple: Panic attacks. Doc told me to cut out any caffeine since the increased heart rate triggered attacks. I got it under control again but still haven't touched caffeine. I miss coffee a lot, I was a lot more productive with some caffeine in my body.
I have a similar cause-effect with caffeine. I can drink a coffee in the morning before 10am and feel great because I’m still somewhat asleep - but an afternoon coffee is too much and overstimulates me. I find that alcohol can have a similar effect too!
