Here is a link to a video I found at Internet about how to stop relapse of depression in the beginning. The point is that after about two depressive episodes (some says only one), the chances of having a new episode comes with it, and then a new and a new one.

I have discovered this myself, even if I thought in former years that to overcome depression was only to do once. If we look out for symptoms that can be the start of a relapse, it can hopefully help us to stop a full blown up episode. :-)