I would not say that there are similarities between mild depression and spiritual progress, but mild depression can lead to spiritual progress or awakening as the discontentment and pain associated with depression may lead you on an inward journey to find relief.
That is what happened to me, but it took me 4-years to understand the real source of my depression. Pretty much by accident, I learned that my negative and destructive thinking was causing self-hate and unhappiness. It wasn’t until I became aware of this and then began to take action, mostly through meditation and other healing techniques that I was able to quiet my mind which in turn healed my depression.
It wasn’t easy, but I did it. This spiritual awakening lead me to dig deeper into the things of the mind and spirit and thus as you stated, helped in my spiritual progress. Negative emotions reveal that something is amiss in our internal environment and with that awareness we can make new choices on how to think. You might be interested in learning more about meditation and how it can heal your life. Christian Meditation- What Do You Need to Heal? .
If you would like, please join my Christian’s Who Meditate Facebook Group!