I've felt the darkness inside for almost two decades now. It hasn't gone but I've learned to...as the young kids say, "vibe" with it. It exists inside and I know it's there, but I put up roadblocks that are a combination of coping mechanisms that I've learned in therapy and things that I came up with. I still have moments when I drown, but not as often as before.
One of my favorites is, "this time tomorrow". Basically you give it a deadline, it doesn't have to be exactly tomorrow. This started when I was overwhelmed with school work in university; I realized that this time after the deadline(usually the next day because I would procrastinate) I wouldn't be feeling this way, so why go through the experience twice? It's not an all-around roadblock but it allows me to put things into perspective.
Do you have access to a therapist? Even though I didn't like the ones I had, I did learn coping mechanisms that helped my days go by better. These skills will help you rise above the darkness and ride the waves.