How do you know that caffeine was the cause?

This of course cannot be generalized, but withdrawal is quite noticeable for personal well-being in a positive way.

I didn't say it was the cause of the mental health incident! And I don't believe it to have been "the cause", either. It just happens to have been the thing that caused me to abruptly stop.

It likely was a contributor, insofar as the incident had poor sleep as a contributing factor, and I do know with some certainty the caffeine habit had been causing some (likely not all) of my sleep problems. I can also tell you the very worst day of that incident was when I mistakenly consumed caffeine again prior to being recovered enough for that to be safe; that was a horrible glimpse at what that drug can do to you when you're in an already very unstable state. Caffeine definitely can aggravate all kinds of symptoms, even when you're in a relatively stable state. It's a stimulant, after all.

But I think caffeine consumption is… only one factor of many in causes of that incident, and doesn't deserve any special blame. The relevance of the mental health incident here is really that it gave me a chance and a good reason to abruptly stop, and therefore also the opportunity to see what getting the brain back into the caffeination ritual again feels like. (I've tried taking it for a few consecutive days more than once since then, and not particularly enjoyed it. I've also tried it on single isolated days.)