Ah yes brainfog. As someone who writes a lot, I quickly learned brainfog is a writer's absolute arch nemesis, like the devil if writing itself was a religion. I'll be half-way through writing something, fall asleep, then wake up and be unable to piece a concept together. No wonder the first Lord of the Rings took twelve years to write.

I would recommend taking a walk. You may say you're too depressed to take a walk, but it's the other way around, taking a walk can help with feeling depressed. The other two most helpful things for feeling depressed and brain fog are water (as in showering and staying hydrated) and getting eight hours of sleep each day when possible. And then just cycle those three things.