I'm extremely caffeine sensitive, and coffee does indeed induce something in me that looks a lot like hypomania, I can get very agitated and it can be very difficult to stop chattering away. I do initially feel quite a mood boost and coffee can help me get a lot done. It also makes my anxiety much worse. I have a cup of coffee 2 or 3 times a year as a special treat, but drinking it regularly is disastrous for me.

I do have a diagnosis of bipolar II rapid cycling, and an anxiety disorder.

Not sure if that's helpful to you, meow, but that's my experience with coffee.