I was depressed and often suicidal for five years. During that time, there was little decrease in my production of words as a writer. You'd think if you were just checking up on how many books I was writing that I was fine. I looked fine in many ways. I continued to manage daily chores: laundry, dishes, food preparation. I exercised six days a week and competed in a lot of races, including some Ironman distance races. But I was still depressed, and I knew I was depressed. Maybe this helped save me in some way. I'm still figuring things out.
What I can see very clearly now is that what was wrong with my creativity wasn't my ability to make books or craft scenes or envision new worlds. My creativity worked fine on that level. Writing actually allowed me to get out of my own head and was therapeutic in certain ways. But the problem was that because my brain was broken, and in particular, because my judgment was broken, I couldn't make good decisions about what books to work on. I couldn't make any decisions myself about my life or my career because I knew my judgment was compromised. I kept delaying making decisions because I didn't want to make a big mistake, and I didn't trust myself.
People who imagine that depression is good or even necessary for creativity can't have really being either depressed or creative. There may be a correlation, but it isn't causative. When I see depressed creative people around me, they don't always have the same problems I had with depression. Many of them simply stop writing at all. Whatever joy they had in writing is gone and they can't find a good reason to deal with the other difficulties of writing when that's gone. There are also the creative types who try to keep at it, but then burn everything in despair, because they can't see anything good in what they've done. I've seen this and it is heartbreaking. It happens a lot, though.
If there is a correlation between creativity and depression, it may be simply that creative people often feel things more deeply, both good and bad. And also, creative people are often isolated, which is something that causes depression in pretty much everyone, creative or not. There are risks to being a creative person. Creative people invite more criticism. They also lay themselves on the line more in their writing. This is painful in ways that perhaps only other creative people can understand. But depression isn't good for your creativity.
If you are depressed, please get help. Maybe you need a group that meets regularly to talk about the work. Maybe you need a therapist. Maybe you need medication. Maybe you need some life changes to help you see the world and yourself differently. Please, don't imagine that any of these solutions will do anything but improve your creative output. Depression isn't what makes you you. It isn't the way you really feel the depth of human emotions. It's an obstacle. Your creativity should improve when you deal with it. If you think it won't, just remember, depression means your brain isn't working right. It's not giving you the right information about itself, or about anything else.