Antidepressants. Venlafaxine is quite good - there are no initial side effects. You might try a herb - St. John’s Wort but for me, it wasn't strong enough. Lifestyle changes can help but sometimes they aren't enough.
I'm going to try to push this towards the back of the list because I don't have health insurance... I was on antidepressants when I was severely injured and I do remember being in a fairly good mood in the months I stayed in the hospital despite my circumstances. I encourage anyone reading this in the future to consider this as a viable option.