I'm wary of giving & taking medical advice on the internet; and so should you be too.
But I'll just pass on my experience: as an anecdote.
Try sitting by a waterfall for a couple of hours
Years back now I was feeling permanently a bit shit, I was still doing a bit of fishing though and one day, having been out fishing off the dam at a small pond, I came home, had a tin of Heinz tomato and an orange and went to bed. I woke up the next morning feeling as if my mental curtains had been drawn back, the windows flung wide open and a new spring day had been let into my room.
I tried the soup and oranges again thinking, vitamins, bright colours, but it wasn't that.
In later years I noticed the same thing whenever I visited that same small pond: I thought maybe it's just being out in the fresh air, miles away from traffic fumes.
It also reminded me that decades back my mate had a room deionizer and when left on overnight all the smoke and beer fumes had gone and in the morning the room smelt like sitting by a waterfall.
I was reminded of this more recently: another session at the same lake, sitting by the outflow (trying to) photograph wagtails; and again working down there in the same spot for an evening cutting back some undergrowth and fallen branches: both times I woke up the next morning feeling totally refreshed. A new day.
I should maybe mention now that the sluice on this small lake tumbles down over a 12-15 foot high waterfall. I had always been thinking in terms of the falling water ionizing the water and producing something like that room di-onizer which somehow overcomes any feelings of depression but never had enough (or thought upon it long enough) to tie all the bits together.
I took the BBC article (which mentions waterfalls) linked to above as another link in a possible chain.
Cold water swimming does wonders for mental health too, caveats apply but it does create one hell of a WOW moment.
All the best with yours; I used to go to bed and just say, "this feeling won't last forever, this feeling won't last forever" . Later I realised I wasn't saying it: I don't think it's passed, it just doesn't dominate any more.