Coffee Withdrawal Syndrome

I have stopped drinking coffee for 3 days now.
I decided to do this 4 days ago when I realized my heart was racing.
I usually down 3-4 cups a day.
I was incredibly irritable and grumpy on the first day of abstinence.
I was also so very tired.
Lack of concentration as well.
I believe my colleagues felt it.
I gave them one word answers.
I emanated the stop-bothering-me vibe.
The positive effects of not drinking coffee came almost immediately.
My heart-beat was back to normal.
I felt better.
I looked it up and I do believe...
I had an out-of-coffee experience.