I suffer from depression, too. I can relate to that black cloud of despair.
I find that I have the most energy first thing in the morning. So, if there is a time when you typically have a lot of energy, capitalize on that. For me, it's 6:30 a.m. I get to the office 2 hours before anyone else. No one calls that early, so there are no interruptions. I can literally get more done betwen 6:30 a.m. - 8:30 a.m. than I can between 8:30 a.m. - 4:30 p.m. Then I don't feel bad if the rest of the day is unproductive.
It wasn't long ago that I hit a real low. What I had to do was just simply focus on ONE THING that I wanted to get done. I absolutely, positively, had to load the dishwasher. It took me all day to do it, but once I convinced myself to do it at 7:30 p.m., I was able to say to myself, "I'm proud of you!" and get a good night's sleep and start over the next day.
I hope this helps!