Wholly anecdotal, but as a 52 year old nearly-lifelong caffeine (ab)user I quit this year and the withdrawal period was horrendous -- not for the headaches everyone knows about (they were bad but only lasted a couple of days) but for the somewhat extended depression/anhedonia which I had never really experienced before.

I was worried during that stretch of time that maybe the caffeine had been masking some underlying depression I already had, but a couple of weeks in it passed, so I think my brain just needed to rebalance itself to the new caffeine-free reality.

I'm glad I quit (less anxiety, better sleep, I'm finding it a lot easier to eat healthy while not buzzed on caffeine all the time, and the depressive episode was temporary) but going through that makes it pretty easy for me to believe caffeine can have rather powerful effects in this area.

I think a lot of the difficulty in quitting can be mitigated by slowly titrating down the dose over a month or two instead of quitting cold turkey.

But your experience mirrors mine in going cold turkey which I think demonstrates that caffeine can cause both physical chemical dependence, and psychological addiction.