Depression can come from many directions but for me it is merely a lack of light and once I can see cause I can use my energy sprays (Similar to flower essences) to clear it. The effect can be instant but I find that I do need to keep working on to prevent it coming back. It can be your own energy block or event causing this or something in the wider environment or picking up energy from friends and family which can be the cause. Its hard to find out the source and its not easy to be certain but you can try and narrow it down especially by seeing what makes it clear and when does it come back.
Usually its a block in the heart or an over active mind, or over focus away from yourself on something / someone who lacks the light. This blocks out the light coming in from above the crown. It can be many things but they are the most obvious causes.