I'm not an expert, but I thought I'd share what came to mind. Jung touches on something similar in his work. He theorized we go through trauma and then dissociate from it as a protective mechanism. The various sub personalities then live on subconsciously and reappear as we experience similar situations in the future. Re-integration of these dissociations is his recommendation. This type of therapy is one way of going about it. I've been doing something similar on my own for a while now.

The thought I had was that it may be easier to connect with pieces of yourself like 'misery' when you are in a depressed like state. I imagine it might be harder to connect with the root of something like that if you were feeling normal or in a manic state. Perhaps you can leverage that perspective and see some light in your depression as a tool to allow you to bring some of your more depressed sub personalities forward? In my mind, shifts in mood and the resulting experiences are all catalysts for change. The way we choose to use them defines the outcome.