What helped me more than anything was going out into the garden and digging. I made sure to do it safely, since I know it can be risky, so I dug wide and with wooden supports, but there was something about just digging and digging down that let me work through all the darkness that had built up in my head. It gave those feelings somewhere to go.
This is unrelated, but I wonder if I did actually hit on something primal in myself.