I did not suffer severe depression. Mine was a chronic depression that lasted a couple of years (sort of like a chronic backache, it's not bad enough to require hospitalization, but is a constant source of pain). In my case, I learned to cope with Vipassana (Insight, or Mindfulness) meditation.
There are a few ways Vipassana helps one deal with depression. In my experience, they all work simultaneously.
One way is that it clears my mind and put me in a much better position to see the source of my problems. For example, I was no longer overwhelmed by a general sense of "depression", I could clearly see each component cause. I'm feeling this way coz I'm experiencing shock, fear, sadness etc etc. I experience shock coz of my expectations of this and this. I experience the fear coz I feel helplessness and uncertainty. etc etc.
Seeing clearly how each feeling contributed to my "depression" helps a lot coz it gives me a direction of how I should approach my problem. For example, I deal with the fear component by working with the uncertainty component. I deal with the uncertainty component by re-evaluating my situation. And slowly, having dealt with that, my fear begins to be solved. And so on.
The second and perhaps the most powerful way Mindfulness helped me was that it kept me "above" my problems. In Mindfulness, I saw one of the biggest causes, if not THE biggest cause, of my sufferings. In one word: Aversion. I felt very adversed to unplesant feelings and states of mind. I could feel my mind rejecting the situation, the "this is not fair!" and "why me?" feelings. I didn't want it to be this way, I wanted things to be "right".
Here, I discovered how important the First Noble Truth is. In life, the first mistake we make is to expect to have no problems, that everything is going to be OK. When people think this way, when they have problems, their sufferings double coz they keep thinking, "it shouldn't be like this. Everything should be ok. I should be feeling good".
I discovered tt the first step to solving problems is to acknowledge and accept them. I'm human, it's perfectly normal to have problems. I accept that, as a human, I will feel pain. I mindfully, peacefully and compassionately acknowledge and accept the pain as part of my life.
With Mindfulness, I let go my clinging to the "I should be feeling good" desire. I fully experience and observe my emotions and experiences. I allow Aversion to fade away. There is no clinging. There is only feelings as they are. This state of mind is very peaceful. This peace allowed me to "stay above" my depression and it allowed me the space to work with, cope with, and solve my problems. A very powerful experience for me.
Finally, Mindfulness also helped by allowing me to stay calm and composed. This has to do with the physiology of emotional pain. When we'r experiencing emotional pain, such as depression, our body reacts as well. We feel tightness in the head, neck and stomach areas. Our blood pressure & heart-rate gets affected. There is a general sense of unease in the body, which in turn interferes with our minds. With Mindfulness, we can fully experience our physical discomforts & come to terms with them. Many times, it somewhat soothes the physical discomfort & helps us feel a little better.
In my case, talking to people helped a lot too. Mindfulness allowed me to see my own problems clearly, allowing me to communicate my problems better with the people I'm close to. It helped a lot.
To end this article, I agree that while Mindfulness meditation helped me a tremendous lot, it might enhance the depression for some people, esp if the depression is too strong for the meditator to handle or if it involves some sort of traumatic experiences. In such cases, I would suggest tt one seeks guidence from a qualified psychologist or a qualified Vipassana teacher. I'm just an ordinary man, I'm unqualified.