An assortment of principles and guidelines.
Accept that you have lost the ability to control your mood. Accept that you have to accommodate your mood's whims. You need energy to work and energy flows from your mood. When in a dark mood and working, attempt tasks that require the least creativity and imagination, such as processing receipts and organising books on the bookshelf.
Either work and feel terrible or avoid work and feel good, but don't let yourself avoid work while feeling terrible. If you simply can't work, then focus on feeling better, and if you don't know how to feel better, then find some significant, non-creative work and start doing it.1
Focus on a single next action. Ruthlessly ignore the future. Nothing else matters right now.
Go with your energy.2 Do what you feel like doing, even at the expense of something that you need to do.
Accept that you will let some tasks become alarmingly urgent before you finally do them. Accept that you will probably fight fires. Feel the shame, then let it go.
Ruthlessly ignore doing what you think you "should" do. Focus on what you must do and what you value doing. You can expect not always to like doing what you value doing.
Avoid commitments. Refuse commitments when others try to force them on you. Look for self-contained opportunities to contribute where completing the work helps people but not completing the work does not hurt them. Do not sign up for multi-step projects.
Back out of commitments as soon as you realize that you no longer have energy for them, even if you value them and even if you people are counting on you. Do so humbly and apologetically. Feel the shame, then let it go.
Look for any opportunity to build more slack into your life: money slack, time slack or energy slack.
Fight against isolation, even though you will feel the impulse to withdraw. Even if you isolate yourself in your work, you must find other ways to connect with other people. Almost any kind of connection will help.
You might feel ashamed or frightened to talk about depression. I don't feel nearly the shame or fear that I used to. You can tell me what's on your mind by visiting tell.jbrains.ca.
Everything else I read on [this] topic has falls into one of two categories; (a) advice on how not be depressed and, (b) general productivity advice. When realistically, (a) the situation is that right now I am suffering depression (and might be prone to again in the future?) and life continues, so I'm seeking the ability to maintain a functioning level of productivity, and (b) I'm generally fully aware of what I need to do and how to organise myself, but simply unable get past the paralysis, to break the catch-22 and actually do it.
Your thoughts were refreshingly relevant, and practical. Thank you.
—An anonymous reader
Tom DeMarco, Slack: Getting Past Burnout, Busywork, and the Myth of Total Efficiency. You need slack in order to accommodate your moods, so you'd better make creating slack a centerpiece of your life strategy.
Gitte Klitgaard, Stress and Depression: A Taboo in Our Time. 27 minutes of video. I attended this conference talk live and felt so relieved to see someone willing to talk about this on stage. I also felt good keynoting at a conference that would support this kind of discussion.
Maria Popova, "Henry Miller's 11 Commandments of Writing and Daily Creative Routine". I see some of Henry Miller's advice as slightly over-prescribing, but I really appreciate the spirit of his suggestions.
Steven Skoczen, "What To Do When You're Depressed". I recommend reading this to feel better about your situation, at least a little. I learned a lot of these lessons on my own, and I'm not convinced that reading them would have stopped me from needing to learn them all on my own, but that might have helped me, so it might help you.