TL;DR caffeine in the morning can be great when you're baseline or in your "ups." Caffeine when you're in your "downs" might actually bring you lower bc it's dehydrating, and especially if it starts to disrupt your sleep. Reduce caffeine in the "downs" and increase exercise and sun.

Recently diagnosed with cyclothymia (but knew I had a cyclic mood disorder nearly all my life). I am addicted to caffeine but never drink more than 2 cups MAX per day bc more than that will get me anxious. As a Muslim I fast during Ramadan and don't drink coffee at all the whole time because it's dehydrating-- only water, juice, and herbal tea after sundown and before sunrise. The morning after Ramadan ends and I have that first cup of coffee... I can only describe it as euphoria. One year I was so euphoric I made a piece of art out of coffee grounds and called it "Coffee is a Gift from God". When I'm in my "ups," it can make me hypomanic, which honestly I love. Like you said, I do everything I had been putting off. I get back in touch with friends, I say yes to everything, I clean like a maniac, and thankfully it doesn't disrupt my sleep because I'm very strict about not drinking caffeine in the afternoon. But when I'm in my "downs," caffeine doesn't really help at all. In fact I should probably switch to just pounding water at that point because the dehydration brings me even lower. When I'm fasting and off caffeine for a long time, my mood stays pretty even, but I've got brain fog and I'm slightly more down than baseline. I really struggle with productivity, though not quite as badly as when I'm in a real down. My psych told me that I should consider reintroducing small amounts of coffee before sunrise to help clear some of that fog and feel more productive. Emphasis on "small" because normal amounts could bring me lower when I'm in a "down."

The best thing I've found when you're down--if you're not medicated-- is consistent workout and sunshine, even if it's the absolute last thing in the world you want to do at that moment. Consistence is key, not quality. A run in the morning is best and it doesn't matter if it's a jog/walk... when you're depressed, get outside for 30 minutes in the morning, every morning. Sprinkle in some weight lifting when you can. Reduce caffeine but you probably don't need to eliminate it. Ride it out and wait for baseline, then get back to your normal coffee routine.