@lioness @parus; @herbnj - I often have wondered the same thing - I have felt so great-now what? Even if we are not aware of them everything has a trigger, what sets things off..Something said that we only half heard, a picture of an old friend, or feeling neglected by everyone. These are warning signs and a red flag should go up.
This article will help: https://www.healthline.com/health/depression/strategies-for-dealing-with-depressive-episode