Mark, I have experienced severe depression once in my life - it came wrapped in a package of grief; truly working on its roots was key to recovery. I found a grief support group, stayed with it for eleven years (nine years as a group facilitator); it was extraordinarily healing.
I see you as 'keenly aware' and sense that you will know when to take steps for treatment if it becomes necessary. In the meantime, working on any underlying issues can bring understanding, acceptance and healing as it did for me.